Belgrade is known as a city at the crossroads of empires, but few know its oldest foundation is stone from Tašmajdan. When Castrum Singidunum was founded by Legio IV Flavia Felix at the confluence of Sava and Danube, soldiers quarried limestone from Tašmajdan to build fortress walls on Kalemegdan, roads, thermae, administrative buildings, and sarcophagi. Tašmajdan became Belgrade’s first industrial center.