Some information about the use of the siege crossbow, the double-bow arcuballista, by the Cham:
“It was when in A.D. 1171 according to Chinese records, Ji Yangzhun was sent from Song dynasty China to Champa to teach the Chams in the use of the multibow siege crossbow. Not long after this date, double-bow arcuballistas appeared in 13th century A.D. Khmer bas relief sculptures on the walls of Bayon (Angkor Thom) and at Banteay Chmar. The Khmer, enemies of the Cham, very possibly adopted the technology from the Chams in their many wars for supremacy over the Indochina region. Siege crossbows were probably used by both the Khmers and the Chams in their wars with each other.”
The double-bow arcuballista:
Source: http://www.grandhistorian.com/chinesesiegewarfare