 According to Philo the width of a wall had to be 4.5 meters thick to be able to withstand artillery.European walls of the 1200s and 1300s could reach the Roman equivalents but rarely exceeded them in length, width, and height, remaining around two meters thick.It is apt to note that when referring to a very thick wall in medieval Europe, what is usually meant is a wall of 2.5 meters in width, which would have been considered thin in a Chinese context.