Plovdiv, population 360000, is Bulgaria's second largest city and has a long history. It was first a Thracian site, which Philip II of Macedon renamed Philippopolis in 342. It was sacked by the Huns in 447, and was sent into decline. Byzantine control of the area was tenuous, especially with the arrival of the Bulgars. In 1206, Bulgarian Tsar Kaloyan damaged the city even further. The Turks gained control in the 14th century, renaming the city Filibe. It recovered as a commercial center, with a rich trading class emerging. In the mid-nineteenth century, Plovdiv's elite promoted Bulgarian culture. This gave birth to a quarter of ornate mansions with cobbled hilly streets. The style used is called National Revival architecture. To solve problems linked with scarce availability of ground, houses expand with each storey.