Göbekli Tepe is an archaeological site atop a mountain ridge in the Southeastern Anatolia Region of modern-day Turkey, approximately 12 km (7 mi) northeast of the city of ?anl?urfa. The tell has a height of 15 m (49 ft) and is about 300 m (980 ft) in diameter.It is approximately 760 m (2,490 ft) above sea level.The tell includes two phases of ritual use dating back to the 10th–8th millennium BCE. During the first phase, pre-pottery Neolithic A (PPNA), circles of massive T-shaped stone pillars were erected, the world’s oldest known megaliths. More than 200 pillars in about 20 circles are currently known through geophysical surveys. Each pillar has a height of up to 6 m (20 ft) and a weight of up to 20 tons. They are fitted into sockets that were hewn out of the bedrock. In the second phase, Pre-Pottery Neolithic B (PPNB), the erected pillars are smaller and stood in rectangular rooms, also with floors of polished lime. The site was abandoned after the PPNB-period. Younger structures date to classical times.