I answered a similar question just awhile ago. A simple answer is, they were aware of each other's locations to some degree of precision, with both sides having sent envoys to the other in the hopes of making direct contact. The Chinese envoy, Gan Ying, came as far as either the Black Sea, the Persian Gulf, or (by a stretch) maybe the Mediterranean, but was dissuaded at the coastline and turned back.
For my more detailed answer, check this link here: