Its quite fascinating and defensive innovations drove alot of interesting architechture. For example machiolations were a response to sapping being used especially by Saracen armies (who seemed to favor sapping more than Europeans) against the Crusaders.
Also the movement from square towers to round ones, once again as a defense for sapping, and displacing the tower from the wall or keep in order to be able to flank assaulters attempting an escalade.
The mastery of stone fortifications made walls nearly impregnable to breaches until cannons were developed, and even by then it was a dodgy proposiiton. For instance at Constantinople in 1453 the Turks had huge cannon which could damage the walls, yet it was not the reason the city fell. The defenders were able to repair the walls before the cannon could reload for a second shot. The reason Constantinople fell was a side gate was left open (either intentionally or accidentally) which allowed the Turks to pour through. There were alot of incidents like this such as the defenders of the Krak de Chevaliers (in modern day Syria) being duped into believing their commander had ordered their surrender
Round towers and concentric design started to become popular in the 13th century which was well before cannon were useful. Cannon were not all that practical until the mid-15th century, which is when you started to see the "star" fort design, and the replacement of stone with earth and brick, lower walls that were more sloped.
Also the movement from square towers to round ones, once again as a defense for sapping, and displacing the tower from the wall or keep in order to be able to flank assaulters attempting an escalade.
The mastery of stone fortifications made walls nearly impregnable to breaches until cannons were developed, and even by then it was a dodgy proposiiton. For instance at Constantinople in 1453 the Turks had huge cannon which could damage the walls, yet it was not the reason the city fell. The defenders were able to repair the walls before the cannon could reload for a second shot. The reason Constantinople fell was a side gate was left open (either intentionally or accidentally) which allowed the Turks to pour through. There were alot of incidents like this such as the defenders of the Krak de Chevaliers (in modern day Syria) being duped into believing their commander had ordered their surrender