Other arrow shooting machines such as the larger ballista and smaller "Scorpio" also existed starting from around 338 BC, but these are torsion catapults and not considered crossbows. Arrow-shooting machines ("katapeltai") are briefly mentioned by Aeneas Tacticus in his treatise on siegecraft written around 350 BC. An Athenian inventory from 330–329 BC includes catapults bolts with heads and flights. Arrow-shooting machines in action are reported from Philip II's siege of Perinthos in Thrace in 340 BC. At the same time, Greek fortifications began to feature high towers with shuttered windows in the top, presumably to house anti-personnel arrow shooters, as in Aigosthena.