Evidence of communal activity in the area around Muscat dates back to the 6th millennium BCE in Ras al-Hamra, where burial sites of fishermen have been found. The graves appear to be well formed and indicate the existence of burial rituals. South of Muscat, remnants of Harappan pottery indicate some level of contact with the Indus Valley Civilisation. Muscat's notability as a port was acknowledged as early as the 1st century CE by the Greek geographer Ptolemy, who referred to it as ''Cryptus Portus'' (the ''Hidden Port''), and by Pliny the Elder, who called it ''Amithoscuta''.