Dacian Fortresses of the Orăștie Mountains, Romania

These six defenses were built over two centuries (from the 1st century BC to the 1st century AD). They constituted the fortified core of the Dacian kingdom until the early 2nd century, when they were conquered under the Emperor Trajan. Most interesting is the fortress of Sarmizegetusa Regia, which is, along with the others, a UNESCO World Heritage Site.