User talk:218.215.153.36

The following is in the article:

"Prior to the Hellenistic Period, towers were largely simple, single-storied square buildings. Due to advances in military technology this style of tower changed. The creation of the canon led to the development of circular or multi-angled towers rather than square shaped. The new shapes made the structure stronger against impact from a cannonball"

However, this article refers to the period of 323 - ca. 30 B.C.E. Cannon do not appear in Europe until circa 1375 C.E.