Trafalgar Square seems an incongruous place to find ‘Ice Age’ mammal bones. Yet beneath Nelson’s Column and Admiralty Arch are fossil-rich deposits of the ‘Upper Floodplain Terrace’ deposited by the Thames during the Last Interglacial, about 120, 000 years ago. Most of the discoveries were made fortuitously during excavations for basements in buildings surrounding Trafalgar Square and in several other places around Pall Mall and St. James’s Square. Here the terrace deposits are up to 9 metres deep; they extend below modern sea level and are made up of layers of gravel, sand and silts interspersed with thinner seams rich in plant fossils. Aquatic molluscs are abundant in the sandier horizons and indicate faster-flowing water in the main channel. The channel and its backwaters were bordered by rushes and sedges, with extensive open grassland on the floodplain that provided forage for hippopotamus and other grazing large mammals. Scattered trees including oak, pine, birch and ash, probably grew on the higher and drier terraces. Of particular note is the presence of several plants (e.g. water chestnut, Montpellier maple) and molluscs that are now extinct in this country being found today in areas of mainland Europe with summers warmer than those of Britain today.