A ravelin is a triangular fortification built outside the main walls of a fortress. It is used to protect the walls from direct attacks and to give defenders more space to mount counterattacks. There are several synonyms for the word ravelin, including bastion, bulwark, redoubt, and fortification. These words all represent defensive structures that are designed to withstand attacks and provide a barrier between the enemy and the protected area. Ravelins were often used in medieval fortifications, but they can still be found today in modern military installations and in historic sites around the world.