Why it looks like this

As Chang'an, capital of the Han and Tang dynasties and eastern end of the Silk Road, this was the greatest planned city of its age: a vast rectangle of wards and marketplaces holding perhaps a million people in the 8th century. Today's streets still obey that ancient geometry — the Bell Tower stands where the main axes cross.

The Ming dynasty rebuilt the city smaller in the 14th century and walled it; uniquely among China's big cities, that wall survives complete — 13.7 kilometres of rampart with moat, wide enough to cycle on top — so the map shows a perfect walled rectangle with the modern city, and the Terracotta Army's emperor's tomb country, spreading beyond.