The first early European modern humans appear in the fossil record about 48,000 years ago, during the Paleolithic era. Settled agriculture marked the Neolithic era, which spread slowly across Europe from southeast to the north and west. The later Neolithic period saw the introduction of early metallurgy and the use of copper-based tools and weapons, and the building of megalithic structures, as exemplified by Stonehenge. During the Indo-European migrations, Europe saw migrations from the east and southeast.