Light went out across Croydon on Monday as the borough marked 100 years since the outbreak of the Great War.
Some of Croydon's oldest soldiers attended a ceremony at the town hall, which joined in the nationwide switch-off by dimming lights and lighting candles between 10pm and 11pm.
St Mary the Blessed Virgin Church in Addington also held a candle-lit vigil.
The church is hosting an exhibition looking at the effect of the war on the village's people throughout August and September.
Councillor Tony Newman, leader of Croydon Council, said: "Today, 100 years ago, the world entered one of the darkest periods in its history and many millions of people lost their lives.
"As we look back at those events with sadness we can still turn on the television to see almost daily examples of ongoing conflict around the world.
Visitors at St Mary's exhibition
"My hope is that by reminding the next generation of the senselessness of war we can go some way to bringing about a more peaceful future."
Events to mark the centenary will continue throughout the next four years.
On September 30 pupils at the Brit School will perform the Muddy Choir, a new play by Jesse Briton telling the story of three young boys from Sunderland who served in the Durham Light Infrantry in 1917 and the humanising power of music.
On September 11 an Armistice Day parade will pass through the town, while on November 14 the London Mozart Players will perform an centenary concert at Fairfield Halls.
Croydon Council is compiling a calendar to promote community events to mark the milestone. Dates can be added by emailing email@example.com
It will also award grants of up to £5,000 to not-for-profit groups to stage relevant events.
Further details are available from Yvonne Gaye on 020 8604 7029 or firstname.lastname@example.org
In pictures: Croydon marks the centenary of World War One
Mayor Manju Shahul-Hameed lights a candle at town hall
Pipers played at the opening of the exhibition at St Mary's exhibition
A visitor looks at a replica World War One poster at St Mary's
The church's exhibition highlights the impact of the war in Addington
Vicar Jeanne Males and Hon Curate Barbara Gentilella at St Mary's