English: Portal Tomb at Altcloghfin, Sixmilesross. This is the remains of an elaborate structure, a type of megalithic tomb in use during the Neolithic or New Stone Age from about 3000 to 2000 BC. It is one of twenty such tombs known in Co Tyrone The tomb has three upstanding stones,some loose ones and a good deal of cairn material raising the area of the site above the level of the field. The most northerly stone is a backstone, the most southerly is a portal stone and the one in between is a sidestone. There would originally have been two portal stones which together with the backstone supported an impressive capstone. This was removed in the past and probably broken up. These sites are sometimes known as Druids Altars because of the large capstones, but they are actually burial places of the people who farmed in the area between 4000 and 5000 years ago.