The first recorded stonethrowers were used by the Macedonian army of Alexander the Great during the siege of Halicarnassus in 334 BC. According to the Hellenistic engineer Philo of Byzantium, the common effective range against fortifications was 150 metres (164 yd) with a load of 27 kilograms (60 lb); at that distance, walls had to be 5 metres (5.5 yd) thick to withstand the impact. Anti-personnel stonethrowers hurled much smaller balls, though arrow-shooters like the scorpio were preferred for these purposes. Super-heavy stonethrowers such as those fielded by Demetrius Poliorcetes in his siege of Rhodes (305-304 BC) threw stones of up to 75 kilograms (165 lb) and could be brought close to the walls in siege-towers. Balls of such size were found in small numbers in the arsenals of Carthage and Pergamon, corroborating ancient reports of their use. The Roman artillery engineer Vitruv provided measurements for even more powerful stone-throwers, but it is not known whether these were ever used in combat. Modern experiments show that smaller projectiles could be hurled at least 400500 metres, while ancient authors record maximum ranges of as much as 700 metres (766 yd).