Athens has been inhabited from Neolithic times, possibly from the end of the 4th millennium BC, or nearly 5,000 years. Iron Age burials, in the Kerameikos and other locations, are often richly provided for and demonstrate that from 900 BC onwards Athens was one of the leading centers of trade and prosperity in the region; as were Lefkandi in Euboea and Knossos in Crete. This position may well have resulted from its central location in the Greek world, its secure stronghold on the Acropolis and its access to the sea, which gave it a natural advantage over inland rivals such as Thebes and Sparta.