Why is there a nelsons column in trafalgar square?

Nelson's Column is a monument in Trafalgar Square, London, commemorating Admiral Horatio Nelson's victory at the Battle of Trafalgar (21 October 1805). The 5.5-metre (18 ft) high statue of Nelson stands on a 46-metre (151 ft) high granite column, and is surrounded by four bronze lions which were cast from captured French guns.

The column was designed by architect William Railton and completed in 1843. It is one of the most iconic landmarks in London and a popular tourist destination.