Blackfish only kept 200 men because he was trying to stretch out his supplies as long as humanly possible, trusting that the huge defensive multiplier that the castle would give would allow him to repulse any assaults on Riverrun while the larger army outside starved.
The rest were released, with some no doubt joining the BWB and others going to their homes.
In terms of how many men House Tully has by itself…we don’t have precise figures, which is a bit of a pain. But my rough estimate – dividing the numbers of Riverlanders present at the Fords by three for the three commanders, would be about 3,500.
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