Britain's most senior sailors have laid wreaths at St Paul's Cathedral and on Lord Nelson's ship to mark the 200th anniversary of the Battle of Trafalgar.
Buglers played and prayers were said at a sombre ceremony in St Paul's, while
a 60-strong Navy band performed during the event on HMS Victory in Portsmouth.
The victory over Spanish and French fleets is being celebrated throughout Britain and commemorated in Spain.
The Queen is due to light the first of 1,000 beacons at HMS Victory later.
The beacons are intended to form a "chain of light" around Britain.
At 1200 BST on Friday bells were rung on Royal Navy warships around the world to mark the moment Nelson went into battle.
'Spirit of Britain'
Second Sea Lord Sir James Burnell-Nugent laid wreaths on the deck of the Victory
and below deck at the spot reputed to be where Nelson died after being shot
by the French towards the end of the battle.
Speaking after the wreath-laying, he said: "This is a very special occasion
for the Navy, a special occasion for the nation, and a special occasion for
the world.
"Nelson is a hero in all navies because most countries in the world have been involved in war at sea."
The 1805 battle is seen as ending Napoleon's plans to invade Britain and establishing British supremacy at sea.
In the battle, a Royal Navy fleet beat a combined French and Spanish fleet,
but Nelson was killed by a French marksman.
First Sea Lord Admiral Sir Alan West laid a wreath at Nelson's tomb in St
Paul's. He said he was amazed how the anniversary had "gripped the spirit
of Britain", adding "it's almost a Nelson-fever going on".
French and UK representatives have attended religious services and a military parade in Cadiz, near to the sight of the battle in southern Spain.
The crew members of HMS Chatham sailed alongside Spanish and French vessels to the exact location of the battle, off Cape Trafalgar, where all three ships laid wreaths in the sea.
Katya Adler, the BBC's correspondent in Spain, says events there have been low-key, commemorating rather than celebrating the battle.
Hero's toast
More than 6,000 events are planned across Britain over the weekend.
After lighting the beacon, the Queen will attend a dinner in the great cabin
of HMS Victory. Her toast to the naval hero will be broadcast live.
As well as a host of such formal activities, there will be thousands of small-scale events, ranging from celebratory breakfasts, to parades, concerts and fireworks spectaculars.
The events will end on Sunday with a parade in London's Trafalgar Square
before church bells peal throughout the UK to commemorate those who died in
maritime conflict.
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