Bronze Age arrowheads. These arrowheads are from the Portalon cave (the entrance cave) to the Cueva Mayor, a cave in the Sierra de Atapuerca foothills near Burgos, Spain. The artefacts found in this cave are mostly from the Bronze Age, with dates from 900 BC to 1690 BC. An upper level also includes remains from the late Roman period (4th century). The limestone caves in these hills, containing many prehistoric fossils and artefacts, have been designated a UNESCO World Heritage Site.