Introduction

Belfast Lough is a deep indent of the Irish Sea into the coastline of Northern Ireland. Its southwestern continuation is the Lagan Valley, which separates the steep scarp ofthe Antrim Plateau (height c. 300 m) from the hills of Co Down (c. 120 m) to the southeast. The River Lagan flows along this broad, undulating valley floor through thick deposits of glacial sands and gravels before emptying into the Lough at Belfast. Eight kilometres southwest of Belfast, the river passes the townland of Ballynahatty, a sandy plateau 100 ha in extent. This was the site in the 4th millenium BC of a small passage tomb, orientated to the northwest (Collins 1954: 48; Lawlor 1918: 16–19). Though now denuded of its covering mound, it provided the subsequent focus for a series of atypical passage tombs utilizing ever smaller settings of stone (Hartwell 1998: 33–6). Shortly after 3000 BC this was followed by a complex of large and elaborate east-facing timber structures (Ballynahatty 5 and 6). These in turn were eventually replaced by the earth and stone hengiform enclosure of the Giant's Ring, built around the original passage tomb.