Qseyr el-Dibsi

 place with historical importance, archaeological site, ancient ruins

Also known as Dibsi Faraj, probably the site of ancient Roman Athis, Late Roman/Byzantine Neokaisareia, and Umayyad Qasrin. An alternative suggestion for identifying the site with Thapsacus (in part because of the seeming similarity of the two names' consonants) has not found acceptance. The site was located strategically close to the frontier with Persia and was substantially refortified in two stages, conventionally identified as Diocletianic and Justinianic, with walls, towers, and four gates. Most of the fortified citadel and all of the lower settlement are now submerged by the waters of Lake Assad, except for an area of higher ground (above 300 m) within the citadel, appearing as a small island. The site was investigated for five excavation seasons by archaeologists in 1972-1974, before it was submerged. While the visible part of the site features minor remains, the more impressive structures explored by archaeologists, including a church and basilica, are now underwater.