sentences:  Furthermore, Dublin Bay provided early settlers with a substantial and easily defended harbour, protected to some extent by treacherous sandbanks, shallows and mudflats, and overlooked by the twin sentinels of Howth Head and Killiney Hill.The first known inhabitants of the Dublin region were hunter-gatherers living during the Later Mesolithic, or Middle Stone Age, around 5500 BC.Shell middens, fish traps and occupation debris, which have been found at a number of locations on and around the shores of Dublin Bay (most notably at Sutton, on Dalkey Island), at the Diageo site at Victoria Quay and at Spencer Dock, which is situated along the northern quays, near the mouth of the River Liffey, indicate that these early settlers lived off the sea.