from Serbia and Bulgaria dated to before 4000 BC, showed that early tin bronze was more common than previously thought and developed independently in Europe 1,500 years before the first tin bronze alloys in the Near East. The production of complex tin bronzes lasted for c. 500 years in the Balkans. The authors reported that evidence for the production of such complex bronzes disappears at the end of the 5th millennium coinciding with the "collapse of large cultural complexes in north-eastern Bulgaria and Thrace in the late fifth millennium BC". Tin bronzes using cassiterite tin would be reintroduced to the area again some 1,500 years later. Caucasus The Maykop culture was the major early Bronze Age culture in the North Caucasus. Some scholars date arsenical bronze artifacts in the region as far back as the mid-4th millennium BC. Eastern Europe The Yamnaya culture was a late copper age/early Bronze Age culture dating to the 36th–23rd centuries BC. The culture was predominantly nomadic, with some agriculture practiced near rivers and a few hill-forts. The Catacomb culture, covering several related archaeological cultures, was first to introduce corded pottery decorations into the steppes and showed a profuse use of the polished battle ax, providing a link to the West. Parallels with the Afanasevo culture, including provoked cranial deformations, provide a link to the East. It was preceded by the Yamnaya culture and succeeded by the western Corded Ware culture. The eastern Corded Ware culture (Fatyanovo-Balanovo culture) gave rise to the Abashevo culture, followed by the Sintashta culture, where the earliest known spoked-wheel chariots have been found, dating from c. 2000 BC. The Catacomb culture in the Pontic steppe was succeeded by the Multi-cordoned Ware culture, and the Srubnaya culture from c. the 17th century BC. Central Europe Important sites include: Biskupin (Poland) Nebra (Germany) Zug-Sumpf, Zug, Switzerland Vráble, Slovakia In Central Europe, the early Bronze Age Unetice culture (2300–1600 BC) includes numerous smaller groups like the Straubingen, Adlerberg and Hatvan cultures. Some very rich burials, such as the one located at Leubingen (today part of Sömmerda) with grave gifts crafted from gold, point to an increase of social stratification already present in the Unetice culture. All in all, cemeteries of this period are rare and of small size. The Unetice culture is followed by the middle Bronze Age (1600–1200 BC) Tumulus culture, which is characterized by inhumation burials in tumuli (barrows). In the