Unit Creation Upgrades
 

Research new fortification types

The rapid development of artillery resulted in a revolution of fortification. Old walls and towers could not withstand artillery fire. Ultimately it was necessary to revise the principles of fortification. Walls were made much thicker; towers became larger and lower, on a level with the wall. Then traditional towers were replaced by round towers or bastions. Casemates inside them took over the part of the defunct overhangs on the walls - shooters fired on the enemy below through the holes in the casemate floor. Ditches and ramparts gained new meanings. A rampart protected the foot and the major part of a wall from cannonballs. However, there was a blind space in front of a tower built in the new style because it was round; thus these towers soon gave way to pentagonal bastions. A wall between bastions was called a curtain. To provide additional defences, further fortifications were placed in front of curtains.