It's clear from surviving inventory lists in Gansu and Xinjiang that the crossbow was greatly favored by the Han dynasty. For example, in one batch of slips there are only two mentions of bows, but thirty mentions of crossbows. Crossbows were mass-produced in state armories with designs improving as time went on, such as the use of a mulberry wood stock and brass; a crossbow in 1068 could pierce a tree at 140 paces. Crossbows were used in numbers as large as 50,000 starting from the Qin dynasty and upwards of several hundred thousand during the Han. According to one authority, the crossbow had become "nothing less than the standard weapon of the Han armies," by the second century BC. Han era carved stone images and paintings also contain images of horsemen wielding crossbows. Han soldiers were required to pull an "entry level" crossbow with a draw-weight of 76kg to qualify as a crossbowman.