How did merchants cross deserts with two-humped camels and desert inns?

They used a very patient animal and a very practical building. The animal was the two-humped Bactrian camel, which has served as a pack animal in inner Asia since ancient times. Its tolerance for cold, drought and high altitudes is what enabled caravans to travel the Silk Road. It can go without water for months at a time, its coat can withstand cold as low as -30 °C in winter and heat up to 50 °C in summer, and its humps are made of fat, not water as many people think. As a pack animal it is virtually unsurpassed, able to carry 170 to 250 kg at 47 km per day over four days.

The building was the caravanserai, an inn that provided lodging for travelers, merchants and caravans. In the countryside these were typically built at intervals equivalent to a day's journey, so a caravan always had somewhere safe to stop and rest. Inside, a central courtyard was surrounded by stalls and rooms for people, animals and merchandise, and water came from a well or fountain.

Together the camel and the inn solved the great problem of the deserts: how to keep people, animals and cargo alive between towns. Camels rarely travel faster than human walking speed, yet for centuries their ability to withstand harsh conditions made them ideal for trade across dry regions. The pace was slow, but a caravan could keep going for months, one day's march at a time.