I know ASOIAF gets mistakes when it comes to some medieval aspects, but lords and kings did have standing garrisons, right? I wonder how one would join this garrison if you're not a knight, and how would one be trained? Why didn't everyone join one if it meant pay, food, and shelter? (if it was voluntary)
Thanks in advance!
Most castles did not have "garrisons" per se. The average castle in Europe was the home of a knight. The "garrison" would be the knight, any of his family (sons or brothers) who still lived at home and were of fighting age, and his servants and retainers (cooks, grooms, falconer, huntsman, etc.) who could be armed in case of need. In times of danger, the villagers would take refuge in the castle and would be armed with the weapons stored there.
Larger royal castles or fortress castles, or the castles of great nobles might have had a garrison in peace time. Even so, these garrisons were often surprisingly small.
For example, here are some of the garrisons for important castles guarding the Welsh Marches in about 1160 (a little earlier than the period you are looking for).
The Pipe roll entries show that Oswestry Castle had a garrison of one knight, two porters and two watchmen between 1160 and 1165 (William Fitz Alan was the lord of the castle, but he was a young child and was a ward of the king. The King appointed Guy Lestrange to administer the Fitz Alan lands, and this is the garrison which Lestrange paid for as shown in his accounts of his guardianship).
The two other Fitz Alan Welsh border castles of Clun and Ruthin seem to have had the same peacetime garrison of 5 men.
The Welsh border castles of Shrewsbury and Bridgnorth, seem to have had even smaller garrisons. Shrewsbury was a royal castle, but about 12 miles from the Welsh border and shielded by intervening castles such as Oswestry. It had a garrison of one porter and one watchman. Bridgnorth, another royal castle, slightly further from the border had a garrison of one permanent year round porter.
In time of danger or war, the troops in these castles would be increased. In the summer of 1165 Henry II used Oswestry Castle as his base for a campaign against Owain Gwynedd (an unsuccessful campaign), and during this summer 200 soldiers were stationed at Oswestry and Knockyn Castles.
Again, in 1166-67, the border was troubled and 40 soldiers were paid for at Oswestry Castle for two years. For 158 days of one of these years another 60 soldiers, paid for by the local barons, not the King, were also stationed at Oswestry Castle. By 1168, the soldiers at Oswestry castle were reduced to 20 and that garrison seems to have remained until 1174.
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