Wood, for instance, can be used to build houses, but it's not all that plentiful on the Arabian Peninsula. However, when it becomes cheaper, thanks to trade, suddenly more people can have better houses. Much of the timber that was shipped in the monsoon marketplace came from Africa, which was kind of emblematic. Africa produced a lot of the raw materials, like animal hides and skin and ivory and gold. The Swahili city-states imported finished goods, such as silk and porcelain from China and cotton cloth from India. Spices and foodstuffs, like rice, were shipped from Southeast Asia, and especially Sri Lanka, where black pepper was a primary export. And the Islamic world provided everything from coffee to books to weapons.