This semi-nomadic lifestyle was probably necessitated by the poor condition of the soils, by that time depleted and rendered infertile because of the preceding centuries of forest burning and extensive exploitation. Globular Amphora were the first culture in Poland known for utilizing the domesticated horse, and swine became important as the source of food. Ritual animal, especially cattle burial sites, often with two or more individuals buried together and supplied with objects as strange as drums have been discovered, but their role is not well understood. Globular Amphora people were involved in the north-south amber trade. Their megalithic burials included ceramics, stone tools and ornamental gifts. The Baden culture in southern Poland was the latest of the Danubian ancestry cultures and continued between 3200 and 2600 BCE. They made vessels with characteristic protruding radial ornaments. A large fortified Baden culture settlement of around 3000 BCE was found in Bronocice near Pińczów. Finally there were still in existence the forest zone cultures, representing the ceramic phase of hunting and gathering communities. Some of them lasted into the early Bronze Age. The major industry of this period was flintstone mining. One of the largest Neolithic (middle to late periods) flint mines in Europe with over 700 vertical shafts and preserved underground passages was located in Krzemionki Opatowskie near Ostrowiec Świętokrzyski. The axes produced from the material obtained there were exported to distant parts of the continent. The Corded Ware culture, in existence in central Europe between 3000 and 2000 BCE, originated most likely from Proto-Indo-European nomadic people of the Black Sea steppes. It was a pastoral culture at least in its early stages, for the most part lacking permanent settlements and known primarily from the burial grounds (a large one with many richly furnished graves was discovered in Złota near Sandomierz). They moved together with their herds of cattle, sheep, goats and horses along the river valleys of southern Poland, but also engaged in flint mining and manufacturing of tools and weapons for their own use and trade. A Corded Ware culture princely burial was found in Szczytna, Subcarpathian Voivodeship. The grave, well-secured three meters below the surface, contained a man's skeleton and a funerary gift collection of highly valuable copper decorations, containers, stone tools and arrowheads.