Below Bar is the informal name given to Southampton's High Street. As the town grew during the 19th century, the medieval High Street effectively expanded north of the city walls and was bisected by the Bargate. This continuation of the street was named Above Bar so, naturally, the existing High Street became informally known as Below Bar.
From Medieval times until the Second World War, Below Bar was the focus of commercial activity within the town. Like many towns, Southampton suffered heavily at the hands of the Luftwaffe and much of the old town was destroyed during 1940.
Since the war commercial focus has moved north of the Bargate and Below Bar has seen somewhat of a downturn.