barrel-vault
vaulted, semi-cylindrical construction used often as roof.

cistern
A receptacle for holding rainwater, but also water transported from elsewhere, in order to keep it stored. The cisterns were either covered eiter open, and they could have more than one compartements.

embrasure (loophole)
Also known as arrow loop or arrow slit, it is an opening that passes through a wall, for use by archers. On the outside it is a narrow slit, usually a vertical one, but it could also take different shapes (e.g. crosslet loops, in the shape of a cross). The splay of the wall on the inside provided room for the soldier, so as for him to move freely and be able to aim better. Loopholes were opened through the battlements but also in various parts of the curtain wall, inside conches. Wider embrasures were opened for fire-guns, namely for cannons.