(CBS News) LONDON --The celebration Queen Elizabeth II's Diamond Jublilee kicks into high gear this weekend.
But another towering figure marks an anniversary Thursday: Big Ben.
Over the years, the name has come to be associated with the famous landmark clock tower overlooking the River Thames.
But, as CBS News correspondent Charlie' D'Agata learned, it actually refers to the clock's bell -- and is actually only a nickname for the bell, which is officially called the Great Bell, and weighs in at 13.5 tons.
That clock began ticking 153 years ago, on this date in 1859.
D'Agata broadcast from the top of the tower on "CBS This Morning" Thursday - the first time any American TV network has broadcast live from there.
He also got an up-close tour, from the man known as the keeper of the great clock, of what makes the icon tick -- and chime, as well as a revealing history lesson.
To get a look yourself and see D'Agata's report, click in the video in the player above.