The same units will retaliate, plus archers, monks, and, if available, ballistae. It's best not to take swords with you, but if there's no other way, use them reluctantly.
An important nuance: if there are few archers, no ambushes, and no Valkyries among the leaders, it might be worth stopping their deployment at some point during the assault to preserve the rest of the troops.

Орден Феникса – харизматический :) лидер