The site around Trafalgar Square had been a significant landmark since the 1200s. For centuries, distances measured from Charing Cross have served as location markers. The site of the present square formerly contained the elaborately designed, enclosed courtyard, King's Mews. After George IV moved the mews to Buckingham Palace, the area was redeveloped by John Nash, but progress was slow after his death, and the square did not open until 1844. The Nelson's Column at its centre is guarded by four lion statues. A number of commemorative statues and sculptures occupy the square, but the Fourth Plinth, left empty since 1840, has been host to contemporary art since 1999. Prominent buildings facing the square include the National Gallery, St Martin-in-the-Fields, Canada House, and South Africa House.