This picture was taken in July of 2011, while waiting to get on a riverboat to see London from the Themes. The Elizabeth Tower, as it’s called on the Parliaments website, was completed in 1859. The tower is often referred to as Big Ben, although Big Ben is the nickname of the Great Bell in the Elizabeth Tower, not the tower itself.
Personally, I’d say that the tower is one of the most known tourist attractions associate to London, if not the attraction most people will remember about London. Your associations may vary from others (and mine), as associations are personal. When I visited London late 2010, I went most of the visit without seeing it. Until one night before dinner, when we had gotten slightly lost, and went out on a bridge while getting in touch with the rest of the group. Further along the Themes, you could see the lights from London Eye and the Elizabeth Tower. In the November darkness, it was a pretty magical sight.