((Since this hasn't been updated in about a day, I think I'll temporarily ignore the five post rule.))
Legend tells that, in the time of the Jhulani Empire, the Southern Desert was once not a desert, but a rainforest, more lush and vibrant than the Kalhani. It further says that the jungle empire of the Jhulani people had more wealth and power in its zenith than all the current nations of the earth, sea, and air combined.
But the empire soon became decadent and prideful. They disdained worship of the gods, and instead began worshiping their own emperor as a deity. And so, as punishment, Crysilia, the rain goddess, vowed that the lands of their empire would not receive so much as a drop of precipitation ever again. Without rain, the Great Southern Rainforest soon dried out and became only so much kindling in the sun. It burned up in a great inferno (the soot of which ultimately formed the Ash Islands), taking the once proud Jhulani Empire with it.
A few tiny villages were able to avoid the fire, however, and now act as oases for caravans heading for the southernmost nations, since they have underground reservoirs of water that are tapped by wells. However, each year they must dig the wells deeper and deeper to get water, and some minor side-routes have been abandoned in the past because the wells in those towns were simply tapped out.
Besides acting as a trade route, the Southern Desert is also of great interest to archaeologists and treasure hunters. Though most of the former empire's surface structures were burnt up in the great fire, many stone structures are believed to have survived the conflagration, though most are now buried in sand.
The Jhulani Empire was also known to have built several elaborate underground structures, which are even further buried. The only way to rediscover most of these places is by extrapolating their location from old maps, which requires a very skilled navigator and a good deal of supplies to survived the trip through the waterless desert. But finding such a structure is often deemed worth it, considering the wealth of information to be found such places and the actual wealth to be found there, as legends say most of the Jhulani Empire's vast treasures are still buried beneath the sands.