Central London by the statue of King Charles I at the junction of the Strand, Whitehall and Cockspur Street, just south of Trafalgar Square. The London Plan defines the "Central Activities Zone" policy area, which comprises the City of London, most of Westminster and the inner parts of Camden, Islington, Hackney, Tower Hamlets, Southwark, Lambeth, Kensington & Chelsea and Wandsworth. It is described as "a unique cluster of vitally important activities including central government offices, headquarters and embassies, the largest concentration of London's financial and business services sector and the offices of trade, professional bodies, institutions, associations, communications, publishing, advertising and the
City of London Bridge, Tower Bridge and the Millennium Bridge. The City's flag flies over Tower Bridge, although neither footing is in the City. The size of the City was constrained by a defensive perimeter wall, known as London Wall, which was built by the Romans in the late 2nd century to protect their strategic port city. However the boundaries of the City of London no longer coincide with the old city wall, as the City expanded its jurisdiction slightly over time. During the medieval era, the City's jurisdiction expanded westwards, crossing the historic western border of the original settlement—the River Fleet—along Fleet