Renaissance Walls are the last upgrade stage of pre-modern defenses in Civilization VI. They represent the elaborate defense systems which Renaissance engineers were forced to devise when gunpowder started to invade the battlefield, and the hitting power of modern weapons became too much for simple Walls to stand.
Renaissance walls can withstand serious sieges from gunpowder-armed units, such as the Musketman (even when accompanied by siege equipment), for some time, but the Bombard will quickly wear them down. If you see an army with this type of unit, do your utmost to prevent them from using it!
Note that nations which are good at Civics progression might want to jump straight to Civil Engineering, which will automatically upgrade all city defenses to a post-Renaissance stage. These will ensure a much better protection than Renaissance Walls.
Historical Context Edit
When cannon came to combat, those old, high, straight city walls didn’t stand up very well. Thanks to the unrelenting warfare in Italy during the Renaissance, military engineers there devised the “star fort” (more properly, the trace italienne) in the mid-15th Century AD. The design of a star fortress is evident from any sketch: a flat, low- and thick- and slope-walled structure composed of many triangular bastions, so positioned as to provide covering fire for each other, all surrounded by a glacis to deflect cannonballs and a ditch to deter infantry. Star forts were used by Michelangelo in his defensive designs for Florence, and later the concepts were refined by the engineer Peruzzi (for Siena) and by the author Scamozzi. Against the oft-invading French and Hapsburgs, Italian cities soon dispensed with traditional fortifications and surrounded their cities with star forts. The efficacious design spread out of Italy in the 1530s and 1540s to become the standard across Europe by the time of the great military engineer Vauban.