Serica was one of the easternmost countries of Asia known to the Ancient Greek and Roman geographers. It is generally taken as referring to North China during its Zhou, Qin, and Han dynasties, as it was reached via the overland Silk Road in contrast to the Sinae, who were reached via the maritime routes. A similar distinction was later observed during the Middle Ages between "Cathay" (north) and "Mangi" or "China" (south). The people of Serica were the Seres, whose name was also used for their region. Access to Serica was eased following the Han conquest of the Tarim Basin (modern Xinjiang) but largely blocked when the Parthian Empire fell to the Sassanids. Yule summarized the classical geographers: