Complex sentence: Its fortunes have since ebbed and flowed, mainly with the popularity of the southern trade route: sometimes abandoned, as when Buddhist monk Xuan Zang passed through in the year 644, and other timesbustling, as when Marco Polo came by in 1273.
Split into simpler sentences: Its fortunes have since ebbed and flowed, mainly with the popularity of the southern trade route. It was sometimes abandoned, as when Buddhist monk Xuanzang passed through in the year 644, and when Marco Polo came by in 1273.