The peals of London’s iconic clock tower have filled our ears, our movies, and our imaginations for generations. But Big Ben is scheduled to “fall silent” this next week as London undergoes “major conservation works.” According to CNN, it will stop ringing for four years.

Tomorrow, August 21, Big Ben will ring its last until 2021. The repairs are estimated to cost around £29 million, or $42 million.

Stopping the clock is a significant step for London, as the landmark has been keeping time in the capital for 157 years.

“Big Ben falling silent is a significant milestone in this crucial conservation project. This essential programme of works will safeguard the clock on a long term basis, as well as protecting and preserving its home,” Keeper of the Great Clock, Steve Jaggs, said in a statement.

Looking at the clock tower’s history, Big Ben is actually the name of the bell within the tower. The tower itself was called the Clock Tower, then the St. Stephen’s Tower by Victorian journalists when MPs used to sit in St. Stephen’s Hall. The tower was renamed the Elizabeth Tower in 2012.

According to BBC, the Great Bell weighs 13.7 tonnes, while the tower itself stands at an impressive 96m (315ft) tall. In order to undergo repairs, the clock’s striking hammers will have to be immobilized.

It is also fun to know that, at the top of the hour, the clock strikes an E note.

The bell has fallen silent before. In 2007, the clock underwent some maintenance. But before that the clock had not been silent since 1983, when it stopped ringing for two years during refurbishment.

London officials have assured city residents that the bell will “continue to chime for important national events.”

Parliamentary authorities say that stopping Big Ben from ringing is important for the safety of the workers doing repairs on the clock.