The Dilmun Burial Mounds () are a UNESCO World Heritage Site comprising necropolis areas on the main island of Bahrain dating back to the Dilmun and the Umm al-Nar culture. Bahrain has been known since ancient times as an island with a very large number of burials, the (originally) quite a number of square kilometres of mounds were said to be one of the largest cemeteries in the ancient world. The cemeteries are concentrated in the north of the island, on the hard stony areas slightly above the arable farming soils – the south of the island is mainly sandy and desert-like. Recent studies have shown that the estimated/approximately 350,000 ancient grave mounds could have been solely produced by the local population over a number of thousands of years. The graves are not all of the same era, or of exactly the same styles, and can vary considerably in size in different areas of the moundfield. Research, under the auspices of the Bahrain National Museum (with the Bahrain Historical and Archaeological Society taking a keen interest), is still continuing, to establish a firm timeline for all these variations and continuations, as well as considering the implications for the society or societies that produced them. Excavations Between Sunday the 10th and Tuesday the 19th of February 1889, some of the mounds were excavated by the British explorer J. Theodore Bent and his wife Mabel Bent. According to the diary of Mrs Bent they found “… bits of ivory, charcoal, ostrich eggshell…”. These finds are now in the British Museum, London. Theodore Bent published his results in two articles, but a more extended account appeared in the Bents' book Southern Arabia (1900). A Danish group in the 1950s was excavating at Qal'at al-Bahrain, the capital city of the Bronze Age, when they opened some tumuli and discovered items dating to around 4100–3700 BP of the same culture. Many others began to excavate more of the graves, providing a view of the construction and content on these graves. Chambers (tumuli) Each of the tumuli is composed of a central stone chamber that is enclosed by a low ring-wall and covered by earth and gravel. The size of the mounds varies, but the majority of them measure 15 by 30 ft (4.5 by 9 m) in diameter and are 3–6 ft (1–2 m) high. The smaller mounds usually contain only one chamber. The chambers