The Chinese campaigned in Central Asia on several occasions, and direct encounters between Han troops and Roman legionaries (probably captured or recruited as mercenaries by the Xiong Nu) are recorded, particularly in the 36 BCE battle of Sogdiana (Joseph Needham, Sidney Shapiro). It has been suggested that the Chinese crossbow was transmitted to the Roman world on such occasions, although the Greek gastraphetes provides an alternative origin. R. Ernest Dupuy and Trevor N. Dupuy suggest that in 36 BCE," Han expedition into Central Asia, west of Jaxartes River, apparently encountered and defeated a contingent of Roman legionaries. The Romans may have been part of Antony's army invading Parthia. Sogdiana (modern Bukhara), east of the Oxus River, on the Polytimetus River, was apparently the most easterly penetration ever made by Roman forces in Asia. The margin of Chinese victory appears to have been their crossbows, whose bolts and darts seem easily to have penetrated Roman shields and armour." The Roman historian Florus also describes the visit of numerous envoys, which included "Seres" (China), to the first Roman Emperor Augustus, who reigned between 27 BCE and 14 CE: