Among Bahrain's mysterious ancient remains are the thousands of burial mounds that dominate the landscape in the north of the island. The burial mounds were declared a UNESCO World Heritage Site and comprise areas of several necropolises on the main island of Bahrain, dating back to the Dilmun and Umm al-Nar cultures.Bahrain has been known since ancient times as an island with a large number of burial sites; the mounds (originally several square kilometres in size) 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 agricultural soils. Recent studies have shown that the estimated 350,000 ancient burial mounds could have been made solely by local people over several thousand years. The tombs are not all from the same period, nor exactly the same style, and can vary considerably in size in different areas of the mound field. Research, under the auspices of the Bahrain National Museum (with the keen interest of the Bahrain Historical and Archaeological Society), is continuing to establish a firm chronology for all these variations and continuations, as well as to consider the implications for the society or societies that produced them.The best-preserved and most impressive of these mounds are the royal burial mounds of the village of A’ali. These burial mounds, spanning from the Dilmun era (3rd to 1st millennium BC) to the Tylos era (200 BC to AD 300), are unique in their number and concentration. Pottery workshops in the vicinity of the burial mounds have developed organically over the years, allowing craftsmen to incorporate their facilities around the tombs and even use burial chambers as kilns. Potters fire their pottery using traditional methods that have been passed down through the generations. The A'ali West cemetery is located in the village of Buri, but the official UNESCO designation “A'ali West” is justified by the fact that this burial mound field and the A'ali East burial mound field formed a single physical entity partially divided by a large wadi and now divided by the Shaikh Khalifa Bin Salman Road. Together, they total 5,392 burial mounds. The A'ali West cemetery comprises 723 burial mounds. It is one of the last examples featuring the distribution of mounds on the edge of a burial mound cemetery. This makes A'ali West quite exceptional, as most other burial mound fields are confined to their central areas. Compared to other late-type cemeteries, the mounds appear less dense. This stems from the ancient preference of the Dilmunites to build larger mounds at the edges of a cemetery. The sizes of the late-type burials are above average and, relative to their importance, the mounds have been built further apart from each other.The A'ali East burial mound field contains six special-type burial mounds with outer ring walls, considered to be an indication of chieftain burials. Some of them are still visible today. They are therefore the last examples of their type, as most of the mounds with an outer ring wall fell victim to urban development.A larger group of mounds can be found in the south-west corner of the A'ali West burial mound field, and the shape and dimensions differ from the neighbouring Dilmun burial mounds. It can therefore be assumed that it houses Tylos burials. It was common in Tylos times to enlarge already existing Dilmun cemeteries, as well as to reuse larger Dilmun tombs.