Short answers, pulled from the story.
Trafalgar Square opened to the public on the 1st of May 1844. Construction progress had stalled after the death of architect John Nash in 1835 and resumed following new plans by Charles Barry accepted in April 1840.
Architect William Railton won a competition to design Nelson's Column which stands 169 feet tall. The column features a Corinthian order topped by a statue of Admiral Nelson and is guarded by four sculpted lions added in 1867.
The square was initially planned to be named after King William IV but was renamed after the Battle of Trafalgar as suggested by architect George Ledwell Taylor. This battle took place on the 21st of October 1805 off the coast of Cape Trafalgar southwest Spain.
A Christmas ceremony has been held in the square every year since 1947 when Norway presented London with a spruce or fir tree as gratitude for British support during the Second World War. Prince Olav and the Norwegian government lived in exile in London throughout that war.
Mayor Livingstone enacted bylaws to ban feeding birds in the square in 2003 following measures introduced in February 2001 to stop bird seed sales. Westminster City Council passed further bylaws banning feeding birds on pedestrianised areas in September 2007 due to health hazards from droppings.