The Tower of London, one of the UK's leading visitor attractions, is the focus for commemorations of the 100th anniversary of the First World War, which was marked today with lights out between 22.00 and 23.00.

Britain declared war with Germany at 23:00 BST on 4 August, 1914.

Thousands of ceramic poppies have been planted around the Tower in memory of soldiers who fell during the conflict. They form the Blood Swept Lands and Seas of Red art installation which will be opened today [Tuesday 5 August] by the Duke and Duchess of Cambridge and Prince Harry.

Volunteers have worked for two weeks to place 120,000 ceramic flowers in the moat of the Tower. They'll continue to plant them until the last one is laid on Armistice Day – November 11 2014.

In total, 888,246 poppies will be planted, one to represent each Briton who fell during the conflict.

Blood Swept Lands and Seas of Red was created by ceramic artist Paul Cummins who was inspired to by a poem of the same name by an unknown soldier. He worked with a team of artists to hand-make the poppies in a studio in Derby. The installation was conceived in collaboration with stage designer Tom Piper.

The installation is poignant and dramatic and visually illustrates the human cost of the conflict. The Tower appears to be bleeding.

The Tower of London is part of the Historic Royal Palaces group and welcomed 2,289,698 visitors in 2013, putting it at number seven in the top ten visitor attractions in the ALVA ranking: http://www.alva.org.uk/details.cfm?p=423

The poppies, which range in size from one to two feet, will be for sale from the Tower of London website once the exhibition is dismantled, with the profits going to a number of charities.

Find out more: www.hrp.org.uk/TowerofLondon