In 2015, the necropolis was declared a UNESCO World Heritage Site. The town's vast necropolis is carved out of soft limestone and contains more than 30 burial cave systems. When the catacombs were first explored by archaeologists in the 20th-century, the tombs had already fallen into great disrepair and neglect, and the sarcophagi contained therein had almost all been broken-into by grave-robbers in search for treasure. This pillaging was believed to have happened in the 8th and 9th centuries CE based on the type of terra-cotta lamps found "in situ". The robbers also emptied the stone coffins of the bones of the deceased. During the Mameluk period (13th-15th centuries), the "Cave of the Coffins" (Catacomb no. 20) served as a place of refuge for Arab shepherds. Lieutenant C. R. Conder of the Palestine Exploration Fund visited the site in late 1872 and described one of the systems of caves, known as "The Cave of Hell" ("Mŭghâret el-Jehennum"). While exploring a catacomb, he found there a coin of Agrippa, which find led him to conclude that the ruins date back to "the later Jewish times, about the Christian era." Benjamin Mazar, during his excavations of Sheikh Abreik, discovered coins that date no later than the time of Constantine the Great and Constantius II.