On 31 May 1859, the Great Clock at Westminster began ticking. The Great Bell, commonly called Big Ben, was not heard until July.

The clock belonged to the new Palace of Westminster, built after the 1834 fire. It was part of the rebuilding of Parliament, but it also had a public use. It gave time to the centre of London.

The naming can be confusing. Strictly, Big Ben is the Great Bell, not the clock or the tower. Common usage has blurred the terms, but the event on 31 May 1859 was the clock starting to run.

A clock of that size had to do more than look impressive. It had to keep reliable time and be trusted. That gave the project both an engineering and a parliamentary purpose.

On this date, the clock began its work. The bell, the sound and the familiar name came afterwards.