Geography dictated the Silk Road. Between China and the West lie some of the harshest landscapes on Earth, and the routes were simply the few thin lines along which people and animals could survive the crossing.
The great obstacle
At the centre sits the Taklamakan, a desert so forbidding its name was said to mean "go in and you will not come out." No caravan crossed it directly. Instead the routes hugged its rim, splitting into a northern and a southern branch that threaded from one oasis to the next (Kashgar, Khotan, Turfan, Dunhuang) green towns fed by meltwater from the mountains, each a lifeline where travellers could rest, water their animals, and trade.
Walls of mountains
West of the desert rise enormous ranges (the Pamirs, the Tian Shan, the Hindu Kush) crossed only through high, dangerous passes that were snowbound for much of the year. Beyond them the land opens into the oasis cities of Central Asia, Samarkand and Bukhara, and the routes fan out toward Persia, the Levant, and the Mediterranean.
The steppe corridor
North of the deserts and mountains runs a very different road: the steppe, a belt of grassland stretching thousands of miles across Eurasia. Its nomadic horsemen were both a danger to caravans and, at times, their protectors, and when a single power controlled the steppe the whole northern route grew safe and swift.
The sea route
Alongside the overland ways ran a maritime Silk Road. Ships rode the monsoon winds between China, Southeast Asia, India, and the Persian Gulf, carrying bulk cargo that no camel could match. As shipbuilding improved, this sea route drew more and more trade away from the land: a shift that eventually helped the overland Silk Road decline.