THE POSTMEN

Indeed, during the wedding feast in the Great Hall of Winterfell, as his conversation with Lady Dustin is interrupted, Theon reflects:

She might have said more, but then she saw the maesters. Three of them had entered together by the lord’s door behind the dais—one tall, one plump, one very young, but in their robes and chains they were three grey peas from a black pod. Before the war, Medrick had served Lord Hornwood, Rhodry Lord Cerwyn, and young Henly Lord Slate. Roose Bolton had brought them all to Winterfell to take charge of Luwin’s ravens, so messages might be sent and received from here again.

So the maesters do not enter the Great Hall through the main entrance, but are given the privilege of the lord's door. I suppose that signifies that they serve Roose exclusively, and probably that they have some sort of office near Roose's quarters.

Lady Dustin call the maester "grey rats". The expression has already been used, at least in her thoughts, by Catelyn Stark.

“We have no steward,” Maester Luwin reminded her. Like a little grey rat, she thought, he would not let go.

A maester is not, strictly speaking, necessary to tend ravens (consider Sam during Lord Mormont's ranging, Clydas at the Wall). But Sam just had to release ravens from a cage. In Winterfell, the ravens are in the godswood, as Theon can see.

Above their heads the trees were full of ravens, their feathers fluffed as they hunched on bare brown branches, staring down at the pageantry below. Maester Luwin’s birds. Luwin was dead, and his maester’s tower had been put to the torch, yet the ravens lingered. This is their home.

I suppose tending them and determining which one goes to which castle requires a specialist's expertise. A few things are not entirely clear: Why didn't the maesters bring their own ravens? Why do the ravens linger here? This is understandable only if their natural destination is Winterfell. Otherwise they should have flown away. Let's accept that the maesters can instruct the appropriate ravens to fly to their assigned destination and take note of how unusual the situation is with ravens: no single maester is officially in charge of the ravens, which can be accessed in self-service.

It is interesting to recall some of Maester Luwin's words to Bran.

Maester Luwin sighed. “I can teach you history, healing, herblore. I can teach you the speech of ravens, and how to build a castle, and the way a sailor steers his ship by the stars. I can teach you to measure the days and mark the seasons, and at the Citadel in Oldtown they can teach you a thousand things more. But, Bran, no man can teach you magic.”

What does Luwin mean by "the speech of ravens"? Can the maesters communicate in some way with the ravens? Is it a way to give them instructions for the delivery of messages. Does an attachment develop between a maester and his birds?

Is our list of maesters complete? Not quite, as we will see. But, let's first examine this trio.

As it happens, we have a seemingly exhaustive list of maesters in the north. It has been provided by Maester Aemon when he made an appeal for help at the Wall.

The northern lords offered their best hope, so to them Aemon had sent two birds. To the Umbers and the Boltons, to Castle Cerwyn and Torrhen’s Square, Karhold and Deepwood Motte, to Bear Island, Oldcastle, Widow’s Watch, White Harbor, Barrowton, and the Rills, to the mountain fastnesses of the Liddles, the Burleys, the Norreys, the Harclays, and the Wulls, the black birds brought their plea.

Maester Medrick serves House Hornwood. Ramsay is, by right of marriage, the current Lord of Hornwood – which might be disputed by some. Hornwood men rode with Ramsay to Moat Cailin and Borrowton. Certainly, none of them has forgotten what happened to Lady Hornwood, as Lady Dustin tells Theon

And do you imagine the Hornwood men have forgotten the Bastard’s last marriage, and how his lady wife was left to starve, chewing her own fingers? What do you think passes through their heads when they hear the new bride weeping?

Strictly speaking, a maester shouldn't be considered a "Hornwood man". He has no family ties in the Hornwood lands and probably came there as a foreigner. But since Medrick served Lord Hornwood, and Lady Hornwood after him, he had time enough to develop a an attachment to House Hornwood, and he must have been horrified as least as much as everyone else by Ramsay's murder of Lady Donella. We see him with Roose.

As Maester Medrick went to one knee to whisper in Bolton’s ear, Lady Dustin’s mouth twisted in distaste.

There is bad blood between Ramsay and Manderly over the Hornwood lands.

Roose Bolton’s bastard had started it by seizing Lady Hornwood as she returned from the harvest feast, marrying her that very night even though he was young enough to be her son. Then Lord Manderly had taken her castle. To protect the Hornwood holdings from the Boltons, he had written, but Ser Rodrik had been almost as angry with him as with the bastard.

The question of the lordship of Hornwood has long remained unsolved. When Davos is at White Harbor, Wyman Manderly has not yet conceded.

Roose Bolton, who is named our Warden of the North, requires that I give up my claim to Lord Hornwood’s lands and castles but swears my other holdings shall remain untouched.

But Ramsay claims to be Lord of the Hornwood at the wedding, and we hear no protest from Lord Wyman. So I suppose that the Hornwood has passed very recently to the Boltons. So Medrick does not seem to have ever been in service of Ramsay.

Consider the Frey-Manderly fights erupts in the Great Wall. Manderly is then wounded, and, after Lord Locke has called for a maester, Medrick comes as Hosteen Frey still threatens to use his sword on Manderly.

Hosteen Frey’s sword was red almost to the hilt. Blood spatters speckled his cheeks like freckles. He lowered his blade and said, “As my lord commands. But after I deliver you the head of Stannis Baratheon, I mean to finish hacking off Lord Lard’s.”

Four White Harbor knights had formed a ring around Lord Wyman, as Maester Medrick labored over him to staunch his bleeding.

The diligence under danger of maester Medrick makes me think that he is more faithful to Manderly than to his own lord, Ramsay. Indeed, Manderly was the primary antagonist of Ramsay in the Hornwood dispute. At some point, Manderly had to retreat from Hornwood and Ramsay took hold of the castle since he rode south with Hornwood men. The Hornwood banner flew above Barrowton when Ramsay stopped there before besieging Moat Cailin. I tend to think Medrick was with Ramsay at that point, even if a maester is supposed to remain in his assigned castle.

Final conjecture about Medrick. Did he alert the Starks and Manderlys of the treatment suffered by Lady Hornwood at Ramsay's hands? In any case, if Medrick had emotional attachment to Lady Hornwood, who seemed likable from what we saw of her, he must hate Ramsay.

Maester Rhodry serves House Cerwyn. Castle Cerwyn is the closest fortress to Winterfell at half a day's ride.  We first meet them in Robb's host.

“Don’t act the boy with me, Bran,” Robb said. “You know better than that. Only two days ago one of Lord Bolton’s men knifed one of Lord Cerwyn’s at the Smoking Log. Our lady mother would skin me for a pelt if I let you put yourself at risk.”

Lord Cerwyn was taken prisoner by Tywin Lannister at the Red Fork and died of his wounds in Harrenhal.

Maester Rhodry is the probably the one who sent the news of Rickon and Bran's deaths to Riverrun.

“Would that it was. The bird came from Castle Cerwyn, from Ser Rodrik, my castellan.” Dark wings, dark words. “He has gathered what power he could and is marching on Winterfell, to take the castle back.” How unimportant all that sounded now. “But he said... he wrote... he told me, he...”
[...]
“My lady, what is it? Is it some news of your sons?”
Such a simple question that was; would that the answer could be as simple. When Catelyn tried to speak, the words caught in her throat. “I have no sons but Robb.”

Cley Cerwyn was slain alongside Rodrik Cassel and Leobald Tallhart by Ramsay during the battle of Winterfell. Since there has been survivors of the battle, the truth must be known in Castle Cerwyn, including maester Luwin's murder by Ramsay's order.

But the Cerwyns seem to have been spared the Red Wedding. Indeed Roose left them behind,

“No.” Bolton’s voice was soft, but certain. “I left six hundred men at the ford. Spearmen from the rills, the mountains, and the White Knife, a hundred Hornwood longbows, some freeriders and hedge knights, and a strong force of Stout and Cerwyn men to stiffen them. Ronnel Stout and Ser Kyle Condon have the command. Ser Kyle was the late Lord Cerwyn’s right hand, as I’m sure you know, my lady. Lions swim no better than wolves. So long as the river runs high, Ser Gregor will not cross.”

House Cerwyn is now led by Lady Cerwyn, who is in Barrowton with Lady Dustin in Melisandre's vision. Lady Cerwyn signed two letters sent by Roose (see below). She is not present at the Winterfell Wedding, since Theon enumerates the lords who attend the wedding.

Stout and Slate, Whoresbane Umber, the quarrelsome Ryswells, Hornwood men and Cerywn cousins, fat Lord Wyman Manderly ... not one of them had known Ned Stark’s daughters half so well as he.

So Lady Cerwyn is in her castle half a day away from the wedding. She is the daughter of the late lord Cerwyn and still celibate.

Since  that Maester Rhodry serves Roose.  Here is how Rhodry is described just after the Manderly/Frey fight.

“I see you all want blood,” the Lord of the Dreadfort said. Maester Rhodry stood beside him, a raven on his arm. The bird’s black plumage shone like coal oil in the torchlight.

Maester Henly serves house Slate. The name Henly is not uncommon, since there are two (old) Henlys who died at the battle for the Wall. House Slate is a mystery.  We don't even know where is its seat, to which greater house it is sworn. The house is never mentioned among Robb Stark bannermen. It's problematic that the house does not occur in Aemon's list. Perhaps, "young Henly" has been affected by the Citadel only recently. Wyman Manderly says that he does not trust his own maester.

If Stannis wonders that my letters say so little, it is because I dare not even trust my maester. Theomore is all head and no heart. You heard him in my hall. Maesters are supposed to put aside old loyalties when they don their chains, but I cannot forget that Theomore was born a Lannister of Lannisport and claims some distant kinship to the Lannisters of Casterly Rock.

Manderly might have instructed his Slate bannerman to keep a maester that he could trust.  However, I saw no sign of House Slate at the Merman's court. (We could see one Locke there though.)

House Slate is an unknown proposition. The little we know about it is intriguing: its roots might be far is the past and its colors coincide with those of House Stark.

Lady Dustin has a particular "fondness" for maesters. She suggests a little game.

And isn’t it clever how the maesters go by only one name, even those who had two when they first arrived at the Citadel? That way we cannot know who they truly are or where they come from ... but if you are dogged enough, you can still find out.

I have been unlucky in trying to play the game and guess the origin of Rhodry, Medrick and Henly. (There are a couple of older men called Henly who died at the Wall in ASoS. There is a Bracken nephew of the name Hendry. It would be very interesting if Rhodry or Henly were a Bracken. I am tempted to connect Rhodry to maester Kedry sent with Quentyn Martell.)

Since the maesters seem attached to Roose, it's interesting to recall that Lord Bolton has had difficult relationships with maesters in the past. Here is what Roose did when he arrived in Harrenhal.

[Maester] Tothmure had been sent to the axe for dispatching birds to Casterly Rock and King’s Landing the night Harrenhal had fallen, Lucan the armorer for making weapons for the Lannisters, Goodwife Harra for telling Lady Whent’s household to serve them, the steward for giving Lord Tywin the keys to the treasure vault.

When a castle is taken by force, the standard procedure for the conqueror is to spare the maester and take his service. The execution seems to be an anomaly (Tywin Lannister had not executed Tothmure when he took the castle). Such an incident would be the cause of friction with the Citadel. I suppose the Citadel would take the defense of his men, and has some means of retaliation. Recall that Roose took the renegade maester Qyburn in his service, which would alienate further the Citadel, I suppose. Concerning Tothmure, I conjecture that Roose wanted to silence him and found a pretext (and I suspect he put his hands on the treasure vault, and by executing witnesses he could put the blame on Tywin. But that's another story. But silencing witnesses by sentencing them to death or simply cutting tongues is Roose's typical motus operandi).

Let's look now at the maester at the Dreadfort. When Theon gets out of his prison, there is a feast in honor of the lords Karstark and Umber.

The great hall was dim and smoky. Rows of torches burned to left and right, grasped by skeletal human hands jutting from the walls. High overhead were wooden rafters black from smoke, and a vaulted ceiling lost in shadow. The air was heavy with the smells of wine and ale and roasted meat. Reek’s stomach rumbled noisily at the scents, and his mouth began to water.
Little Walder pushed him stumbling past the long tables where the men of the garrison were eating. He could feel their eyes upon him. The best places, up near the dais, were occupied by Ramsay’s favorites, the Bastard’s Boys. Ben Bones, the old man who kept his lordship’s beloved hunting hounds. Damon, called Damon Dance-for-Me, fair-haired and boyish. Grunt, who had lost his tongue for speaking carelessly in Lord Roose’s hearing. Sour Alyn. Skinner. Yellow Dick. Farther down, below the salt, were others that Reek knew by sight if not by name: sworn swords and serjeants, soldiers and gaolers and torturers. But there were strangers too, faces he did not know. Some wrinkled their noses as he passed, whilst others laughed at the sight of him. Guests, Reek thought, his lordship’s friends, and I am brought up to amuse them. A shiver of fear went through him.
At the high table the Bastard of Bolton sat in his lord father’s seat, drinking from his father’s cup. Two old men shared the high table with him, and Reek knew at a glance that both were lords.

So no maester seems present at the feast. I would guess Theon has seen the maester of the Dreadfort for his amputated fingers. We hear of the maester of the Dreadfort much later.

The door opened with a gust of cold black wind and a swirl of snow. The knight of the moths had returned with the maester the king had sent for, his grey robes concealed beneath a heavy bearskin pelt. Behind them came two other knights, each carrying a raven in a cage. One was the man who'd been with Asha when the banker delivered him to her, a burly man with a winged pig on his surcoat. The other was taller, broad-shouldered and brawny. The big man's breastplate was silvered steel inlaid with niello; though scratched and dinted, it still shone in the candlelight. The cloak that he wore over it was fastened with a burning heart.
"Maester Tybald," announced the knight of the moths.
The maester sank to his knees. He was red-haired and round-shouldered, with close-set eyes that kept flicking toward Theon hanging on the wall. "Your Grace. How may I be of service?"
Stannis did not reply at once. He studied the man before him, his brow furrowed. "Get up." The maester rose. "You are maester at the Dreadfort. How is it you are here with us?"
"Lord Arnolf brought me to tend to his wounded."
"To his wounded? Or his ravens?"  
"Both, Your Grace."
"Both." Stannis snapped the word out. "A maester's raven flies to one place, and one place only. Is that correct?"
The maester mopped sweat.

My guess is that maester Tybald was in a cell under the Dreadfort until he left with Arnolf Karstark, as it is hinted that another prisoner is held there at the same time than Theon.

The sound of the lock turning was the most terrible of all. When the light hit him full in the face, he let out a shriek. He had to cover his eyes with his hands. He would have clawed them out if he’d dared, his head was pounding so. “Take it away, do it in the dark, please, oh please.”
“That’s not him,” said a boy’s voice. “Look at him. We’ve got the wrong cell.”
“Last cell on the left,” another boy replied. “This is the last cell on the left, isn’t it?” “Aye.” A pause. “What’s he saying?”
“I don’t think he likes the light.”

I understand the reason for Tybald to be with Arnolf Karstark as follows. There is a maester at Karhold who, I presume, served Rickard Karstark before the war. Arnolf Karstark pretends to want vengeance for the Red Wedding. Arnolf can not make common cause with the Boltons and Freys in full view of the Karstark household. So he can not employ the Karhold maester to send messages to Roose. However Roose needs information from Arnolf, since that is how he is informed of Stannis' moves. Hence Tybald is more useful with the Karstarks than at the Dreadfort.

Before maester Tybald's time, a maester called Uthor was in service at the Dreadfort. He is mentioned by Roose with some fondness. Uthor made the diagnosis for Domeric's death:

A sickness of the bowels, Maester Uthor says, but I say poison.

The death of Domeric is dated by Ser Rodrik as he talks about Ramsay.

“Few do,” she replied. “He lived with his mother until two years past, when young Domeric died and left Bolton without an heir.

So Tybald became the maester of the Dreadfort recently. It's possible that he sent the raven for the Winterfell letter.

Lady Dustin's game is very easy to play with Tybald – obviously a Westerman name, if not a Lannister. Did Roose let Karstark take Tybald because he doesn't trust his maester?

There seems to be a codified ethical behavior of the maesters. Maester Tybald alludes to such a thing.

"Y-your Grace, my order is sworn to serve, we... "
"I know all about your vows. What I want to know is what was in the letter that you sent to Winterfell. Did you perchance tell Lord Bolton where to find us?"
"S-sire." Round-shouldered Tybald drew himself up proudly.  
"The rules of my order forbid me to divulge the contents of Lord Arnolf's letters."

It's interesting to bring the final episode of Theon's conquest of Winterfell. The final conversation of Luwin and Theon might be relevant to the circumstances of the sending of the Winterfell letter, if only to imagine a maester asked forcefully to send a message.

“Send more birds.”
“It will not serve. By the time the birds reach—”
“Send them!” Knocking the platter of food aside with a swipe of his arm, he pushed off the blankets and rose from Ned Stark’s bed naked and angry. “Or do you want me dead? Is that it, Luwin? The truth now.”
The small grey man was unafraid. “My order serves.”
“Yes, but whom?”
“The realm,” Maester Luwin said, “and Winterfell. Theon, once I taught you sums and letters, history and warcraft. And might have taught you more, had you wished to learn. I will not claim to bear you any great love, no, but I cannot hate you either. Even if I did, so long as you hold Winterfell I am bound by oath to give you counsel. So now I counsel you to yield.”

All maesters might not be as exemplary as Luwin, but the maesters seem bound to serve the lords of the castles they have been assigned to. So the duty of maester Tybald is to serve Roose, the duty of maester Medrick is to serve whoever holds the Hornwood, the duty of maester Rhodry is to serve Lady Cerwyn, and the duty of maester Henly is to serve Lord Slate.

However, the rules seem to have been broken by Roose, who has the three maesters at his service borrowed from other places. So, since those maesters have not been assigned to Winterfell, are they bound to obey the current lord of the castle?

It that's the case, the sending of the Winterfell letter has probably followed the same logic as the conversation between Luwin and Theon.

8. The Citadel

The Citadel has not always been a neutral component of Westerosi politics. Two elements seems to tell us that the maesters have been agents of cultural reform in the Seven Kingdoms, even architects of a new world. We have archmaester Marwyn.

The world the Citadel is building has no place in it for sorcery or prophecy or glass candles, much less for dragons. Ask yourself why Aemon Targaryen was allowed to waste his life upon the Wall, when by rights he should have been raised to archmaester. His blood was why. He could not be trusted. No more than I can.”

Based on these elements, it seems that the Citadel worked for the removal of the Targaryens. It is unlikely that every maester was an agent of such a policy. More likely, a small influential group, a secret society at the Citadel, worked for this end. Certain members of this inner circle were sent to serve at strategic positions to further the Citadel's ends.

The maesters worked against the supernatural elements of the Targaryen rule: dragons. In the north, are the heart trees and the old gods compatible with the world they are building? There is a weirwood at the Isle of Ravens. It seems to be sick though.

An ancient weirwood filled the yard, as it had since these stones had first been raised. The carved face on its trunk was grown over by the same purple moss that hung heavy from the tree’s pale limbs. Half of the branches seemed dead, but elsewhere a few red leaves still rustled, and it was there the ravens liked to perch. The tree was full of them, and there were more in the arched windows overhead, all around the yard.

The rookery at the Isle of Ravens is the oldest building at the Citadel. So the Citadel has always coexisted with a weirwood.

The second element comes to us through Barbrey Dustin.

“They heal, yes. I never said they were not subtle. They tend to us when we are sick and injured, or distraught over the illness of a parent or a child. Whenever we are weakest and most vulnerable, there they are. Sometimes they heal us, and we are duly grateful. When they fail, they console us in our grief, and we are grateful for that as well. Out of gratitude we give them a place beneath our roof and
make them privy to all our shames and secrets, a part of every council. And before too long, the ruler has become the ruled.
“That was how it was with Lord Rickard Stark. Maester Walys was his grey rat’s name. And isn’t it clever how the maesters go by only one name, even those who had two when they first arrived at the Citadel? That way we cannot know who they truly are or where they come from ... but if you are dogged enough, you can still find out. Before he forged his chain, Maester Walys had been known as Walys Flowers. Flowers, Hill, Rivers, Snow ... we give such names to baseborn children to mark them for what they are, but they are always quick to shed them. Walys Flowers had a Hightower girl for a mother ... and an archmaester of the Citadel for a father, it was rumored. The grey rats are not as chaste as they would have us believe. Oldtown maesters are the worst of all. Once he forged his chain, his secret father and his friends wasted no time dispatching him to Winterfell to fill Lord Rickard’s ears with poisoned words as sweet as honey. The Tully marriage was his notion, never doubt it, he—”

One could wonder whether Walys was the son of archmaester Walgrave, who has forgotten more about ravenry than most people know. Barbrey Dustin underlines the proximity of the Citadel to House Hightower.

What was the game played by the Citadel? Was the Tully marriage (along with the fostering of Ned Stark in the Vale, the betrothal of Lyanna and Robert) only part of a network of alliances designed to overthrow the Targaryens? Or was is also a way to reform the north and make it alike the south?

We hear often Maester Luwin speak against superstition in the north.

“Maester Luwin says there are no more giants. He says they’re all dead, like the children of the forest. All that’s left of them are old bones in the earth that men turn up with plows from time to time.”
“Let Maester Luwin ride beyond the Wall,” Osha said.

The maester listened politely. “The wildling woman could give Old Nan lessons in telling tales, I think,” he said when Bran was done. “I will talk with her again if you like, but it would be best if you did not trouble your brother with this folly. He has more than enough to concern him without fretting over giants and dead men in the woods. It’s the Lannisters who hold your lord father, Bran, not the children of the forest.”

Maester Luwin sighed. “Woman, by rights you ought to be dead or in chains. The Starks have treated you more gently than you deserve. It is unkind to repay them for their kindness by filling the boys’ heads with folly.”

The relationship of lords and their maesters are codified. We know that all maester swear an oath to serve and counsel. In return, I suppose their lords owe them a number of things, including protection, or at least security. I wonder what happens when a maester is not well treated by the lord he serves. Here is Roose Bolton in Harrenhal.

Tothmure had been sent to the axe for dispatching birds to Casterly Rock and King’s Landing the night Harrenhal had fallen, Lucan the armorer for making weapons for the Lannisters, Goodwife Harra for telling Lady Whent’s household to serve them, the steward for giving Lord Tywin the keys to the treasure vault.

It seems harsh to kill Tothmure for having done what was his duty. As long as the castle has not been taken, the maester is bound to serve the lord in charge. Had Roose Bolton followed the rule, he would have taken Tothmure in his service. Luwin told Theon in Winterfell.

 Even if I did, so long as you hold Winterfell I am bound by oath to give you counsel.

There is reason to believe that Roose executed Tothmure to silence him. So how would the Citadel react in such a situation? Certainly there is concern about the death of Tothmure, and the Citadel has done an inquiry. Something needs to be done, otherwise no maester would want to serve Roose Bolton again. Moreover, Roose took in his service Qyburn, a renegade maester, who has lost his chain.

So the Citadel should bear no love for Roose Bolton, and has blacklisted him, under all likehood. Nevertheless, Roose has three maesters in his service.

I could find a single other moment in the stories when a character had three maesters in his service (Well, except in the story of Thorren Stark's visit to Aegon the conqueror, but that well outside the elements I allow myself to use). It's again Lord Tywin in Harrenhal.

Though ravens came and went every day, Lord Tywin himself spent most of his days behind closed doors with his war council. Arya caught glimpses of him, but always from afar—once walking the walls in the company of three maesters and the fat captive with the bushy mustache, once riding out with his lords bannermen to visit the encampments, but most often standing in an arch of the covered gallery watching men at practice in the yard below.

I guess that one of them was Maester Tothmure. Another one might be Maester Creylen. Perhaps, Tywin brought the other ones to Harrenhal. Why was Tywin in the company of the maesters and the fat captive, that is Wylis Manderly? Did Tywin need three maesters to understand the mysteries of Harrenhal?

We see again three maesters with Tywin in King's Landing.

Three maesters came hurrying forward, to bundle him out through the king’s door.

Let's return to the maesters attending Roose Bolton in Winterfell.

The reason understood by Theon for their presence is that they are needed to send and receive messages through maester Luwin's ravens. A guess is that Roose wants them for their knowledge. Just like Harrenhal, Winterfell has its mysteries. And as we can see in the study of other characters, there is much interest in the crypts of Winterfell among the some of the guests. We know that First Men wrote histories in runes on the sepulcher of their deads (Tristifer in Oldstones). Therefore there are runes to read in the cryps. But we have yet to see a maester reading runes.

Perhaps Roose would mistrust a single maester and prefers to divide and rule. Of course, there is Roose's habit of getting leeched. I wonder if young Henly, which depends from Lord Slate, does not know something about the ancient history of the Starks which is connected to House Slate. Indeed slate (as a material) is a good support for inscribing runes.

There is a simple explanation for the presence of the three maesters in Winterfell. Roose doubts the loyalty of his guests, and he doesn't want them to communicate with Stannis. So he requisitioned the maesters, in quality of Warden of the North. Note that the three maesters are not bound to serve any other lord, but Roose himself. In case of Roose's demise, the title of Warden of the North is vacant, and the maesters return to the service of House Hornwood, House Slate and House Cerwyn.

Let's examine what we can say about the Winterfell letter at this stage, exclusively from the point of view of the maesters.

Suppose that, as said in the letter, Ramsay is in Winterfell after Stannis' defeat, but Theon and "Arya" are still missing. He has learnt a variety of things from the spearwives and Abel, including that "Arya" is to find shelter at the Wall. Hence Ramsay demands, in quality of Lord of Winterfell, that a maester sends the letter to the Wall.

It would seem that several maesters were with Ramsay, Whoresbane, the Ryswells and the Dustins in Moat Cailin. After their surrender the ironmen are told:

“So few. I had hoped for more. They were such stubborn foes.” Lord Ramsay’s pale eyes shone. “You must be starved. Damon, Alyn, see to them. Wine and ale, and all the food that they can eat. Skinner, show their wounded to our maesters.”

But Ramsay's promise is empty, just gratuitous cruelty, since the ironmen are going to be flayed and put on stakes – this is why Ramsay calls Skinner, his favorite torturer. I don't think Ramsay has any maester ready, and the passage says nothing of Ramsay's relationship with maesters. This little deception from Ramsay might illuminate another point below.

Of course Ramsay has employed the service of a maester to communicate with Roose in the past.

Wouldn't it be unethical for a maester to send a letter with a false signature? Surely a minor difficulty, but it complicates the idea that Ramsay did not write the letter. Furthermore Tybald's pair of ravens are destined to Winterfell and not to the Wall (Tybald alludes to the fact that for some exceptional ravens several destinations are available. But he doesn't mention that his ravens are of this extraordinary type.) So, if Tybald sent the letter, he had to survive the battle and to be taken to Winterfell, to make use of one of Maester Luwin's ravens. Not very likely but possible.

So it's unlikely that the raven has been sent to the Wall by someone with Stannis (Asha, Theon, Stannis himself...). Tybald could have sent a raven after he had taken control of Luwin's ravens in Winterfell. But the author would have to give the letter to Tybald and instruct him to send it from Winterfell. I can hardly see why he would agree with the plan, unless under threat.

Of all the maesters mentioned, none, but Tybald, should felt compelled to send a raven by Ramsay's command, and only if Roose is no more. Of course, Ramsay can force a maester to send a raven under threat. Then, how would he know if the maester has sent the appropriate raven?

In any case, Roose seems to have an exclusive relation to the maesters in Winterfell, who attend him, report to him etc. Everything points to their exclusive obedience to the lord of the Dreadfort.

Would the maesters serve Ramsay if Roose were dead? In principle, maester Medrick should serve Ramsay, Lord of the Hornwood, assuming the lordship is undisputed. There is some indication that Roose is not dead, since Ramsay signs his letter as Trueborn Lord of Winterfell, and not with a longer string of titles such as Lord of Winterfell, of the Dreadfort, of the Hornwood, and warden of the North.

If Roose were to depart the castle, as he would logically do after the defeat of Stannis, he would possibly leave a maester with Ramsay.

Note that in the final scene in the Great Hall, just before the escape, both Rhodry and Medrick are present. But there is no sign of Henly, even when maester are needed to help the wounded. Where is he?

Let's leave this disgression aside, and conclude on the subject of the sender of the letter.

Is our list of "maesters" complete? Not quite. I tend to believe another character present in Winterfell might have been the sender, instead of all mentioned masters.