Market roads, long-distance roads, the Grand Canal, and caravan and sea routes all had important ...

ANSWER:
Besides the economic importance of trade to these empires, there were political considerations. The transportation network connected the central cities with the suburbs and outlying areas. The Grand Canal allowed the integration of the Yangzi Valley with northern China and contributed to the economic and cultural development of eastern China. Many routes converged on Chang'an, including the Grand Canal. Chang'an became the center of the tributary system. This city also had over 1 million residents, with restaurants, inns, temples, mosques, and street stalls. The different neighborhoods were walled and locked at night to prevent crime, reminiscent of today's gated communities.