Even though Scandinavians joined the European Bronze Age cultures fairly late through trade, Scandinavian sites present rich and well-preserved objects made of wool, wood and imported Central European bronze and gold. During this period Scandinavia gave rise to the first known advanced civilization in this area following the Nordic Stone Age. The Scandinavians adopted many central European and Mediterranean symbols at the same time that they created new styles and objects. Mycenaean Greece, the Villanovan Culture, Phoenicia and Ancient Egypt have all been identified as possible sources of influence in Scandinavian artwork from this period. The foreign influence is believed to originate with amber trade, and amber found in Mycenaean graves from this period originates from the Baltic Sea. Several petroglyphs depict ships, and the large stone formations known as stone ships indicate that shipping played an important role in the culture. Several petroglyphs depict ships which could possibly be Mediterranean.