Why is the Trafalgar Square important?

Trafalgar Square was set out to celebrate Admiral Lord Horatio Nelson's victory over the French fleet at the Battle of Trafalgar in 1805 which effectively put an end to Napoleon's plans to invade England. The column in the square is topped by a statue of Nelson.
Trafalgar Square was built in Charing Cross, considered the heart of the city, in the early 19th Century (Completed in 1845) to commemorate the Victory of Admiral Nelson's fleet against a combined fleet from the Spanish and French Navies. The battle of Trafalgur was an important naval victory, which decisively showed the power of the Royal Navy in protecting the British Isles from French and Spanish invasion.