In the fields of Bulgaria they are everywhere — hundreds of mounds like huge molehills concealing the gold-filled tombs of ancient kings who left no other trace of their rule. Known as tumuli, the burial mounds are the only remnants of the Thracian civilisation that inhabited the Balkan Peninsula from the 2nd millennium BC to the 3rd century AD. The accidental discovery of a tomb in 1944 revealed that the earthen structures were in fact man-made and that the burial monuments hidden within contained intricately crafted treasures. Experts believe there are more than 15,000 of these tombs in Bulgaria, a tenth of them in the so-called Valley of the Thracian Kings near the central town of Kazanlak 50 km East of Sopot.The Thracians were a people of horse and cattle breeders, metal miners and goldsmiths who are believed to have had no alphabet of their own and left no written records. They believed in the afterlife and the immortality of the soul, and buried deceased rulers with their horses, dogs, weapons, drinking cups and even playing dice. The kings were considered sons of the great goddess Mother Earth and the burial rites were highly symbolic. The most famous tomb in the valley is the Kazanlak tomb, which was the first to be unearthed during World War II and has been on UNESCO’s World Heritage List since 1979. The Thracians built these splendid monumental structures to last forever.