Considered one of the oldest settlements in the world, Balkh was made famous by Alexander the Great when he used it as his base for conquering Central Asia.  The religious history of Central Asia is mirrored in Balkh.  Legend has it that Zoroaster preached here before it became a key link in the spread of Buddhism from India to China (along with Bamiyan).  Later it became an important Christian center, with its own Metropolitan overseeing bishops far and wide, before eventually becoming an Islamic city.  In fact, one of the world's oldest mosques is located in Balkh.  The Timirud city walls surround a surprisingly large expanse, giving us a hint of the incredible size of this once-great city.