When an assault on the fortifications was contemplated, it was often assisted by the use of "siege engines." The most formidable of these was the trebuchet. This was a large counterweight machine. Some have been built in this century to see just what a trebuchet was capable of. One of these modern trebuchets (a twenty foot long model) could throw a 112 pound weight 230 yards, a 550 pound pig 200 yds, and a 700 pound piano 150 yards. Dead animals were often hurled into the besieged city to spread disease, pigs being favored because they were more aerodynamic. A trebuchet used by the crusaders was dismanteled in 1291 at Acre and required a hundred carts to move. In 1304, king Edward I ordered the construction of a trebuchet that took five foremen and fifty carpenters to build. Until the appearance of larger, and reliable, cannon in the 15th century, the trebuchet was the principal tool for hammering enemy walls, towers and gates. The trebuchet was a medieval invention. Medieval military technicians had lost the ability to make catapults, which were somewhat more effective weapons, but were much more complex and expensive.