Completed in 1841, Trafalgar Square's so-called fourth plinth immediately suffered a funding crisis and has been statue-less ever since. In 1999, it became a showcase for new sculpture, and now it's coming into its own with a series of longer installations. First up is Alison Lapper Pregnant, Marc Quinn's marble portrait of a well-known disabled artist. The 12-ton, 9-foot white marble piece will stay until summer, encouraging crowds at the nearby National Gallery to get a different perspective.