The earliest evidence of human activity in the interior of Wicklow dates to around 4,300 BCE. Passage tombs, from the Neolithic period, are the earliest and most prominent feature of prehistoric Irish civilisation in the Wicklow Mountains. These tombs sit on many of the western and northern summits between Saggart in Dublin and Baltinglass in Wicklow, such as at Seefin and Seefingan. Archaeologist Geraldine Stout has suggested they had a territorial marking function, much like modern-day border posts. Other prehistoric monuments to be found in the uplands include stone circles, standing stones and rock art. The presence of standing stones at altitudes suggests they may have served route-marking purposes. The largest complex of hill forts in Ireland is to be found on the hills near Baltinglass.