The full Nelson

`The boy stood on the burning deck/ Whence all but he had fled;/The flame that lit the battle's wreck/ Shone round him o'er the dead." Thus wrote the poet Felicia Hemans about the greatest British naval victory of the modern age.

No, she wasn't referring to Trafalgar - and the boy on the burning deck wasn't an English hero. The verse refers to the less famous but much more significant Battle of the Nile, won by Nelson seven years before Trafalgar; and the boy was the 13-year-old son of the captain of the French flagship. He, his father and most of the 800-strong crew were lost when the ship - L'Orient - blew up in the heat of battle.

It was an extraordinary engagement: the British had been searching for the French fleet all over the Mediterranean. Finally - at 5pm on 1 August 1798 - they caught up with the French at Aboukir, off the Egyptian coast15 miles east of Alexandria. The battle started almost immediately. As darkness set in "the whole hemisphere... was illuminated by the fire of the hostile fleets", wrote one of Nelson's officers, Captain Edward Berry.

By morning, the French had lost 13 of 17 ships, while the British lost none. However, the ship sent back to England with the official report of battle - and the unofficial accounts in countless personal letters - was captured by the French. The result was that many important details about this pivotal battle contained in the crew's letters were lost to posterity - until now, that is.

For at the site of the conflict, marine archaeologists have succeeded in locating the remains of many French vessels buried in mud on the seabed. This evidence is helping historians fill in details that appeared to have been lost forever when the British mail carrier was captured.

Generations of Britons have been brought up to believe that Trafalgar was the greatest naval battle of the period - but in reality Nelson's victory at the Battle of the Nile was a far greater achievement. If the British fleet had lost, the consequences could have been disastrous; Britain would not only have failed to regain control of the Mediterranean, but she would also have lost her influence in the Middle East. France would have been able to take over the Ottoman Empire, control the route to the Orient and even threaten British India.

And if India had been lost - or the trade links permanently cut - Britain's economy, as well as her political prestige, would have been hard hit indeed. And she would have been less able to subsidise the anti-French war efforts of her Continental allies.

What's more, Napoleon's rise to power would have been greatly accelerated if the French had won at Aboukir - for it was Bonaparte himself who was in charge of the French Egyptian operation. Indeed, as a result of the defeat, he was holed up in Egypt for almost two years. The retreat from Moscow in 1812, his final defeat at Waterloo in 1815 and the Battle of the Nile were Bonaparte's three great disasters.

In 1812, Napoleon failed in his bid to seize Russia. In 1815, he finally lost his long campaign to control Europe. But in 1798, his long-term plans to gain control of the fledgling British Empire in India and cripple Britain's imperial plans foundered.

If things had happened differently in Aboukir Bay that August night, then the nascent British Empire might never have survived and reached its later peak of power - and France's imperial fortunes might well have fared much better.

Now undersea excavations - conducted by French archaeologists - are yielding fresh details about Britain's greatest naval victory. A high- tech survey has located the anchors of seven French ships, giving a clue as to their original position.

The new information shows that the French left a wider gap than was previously thought between their line of ships and a group of sandbanks. This crucial error permitted five British vessels to outflank the French fleet - and allowed Nelson to attack Napoleon's vessels from both sides.

The fresh evidence adds significantly to the surviving historical accounts. Ironically, it seems that the British were only able to outflank their enemy because they had the most up-to-date maritime maps of the area - drawn up by the French. Indeed, it was one of the French admiral's vessels that had drawn up the charts in the first place.

The archaeological excavation has also found the physical remains of three of the French vessels - including L'Orient. According to surviving historical accounts, the 2,700-ton French flagship went down after a vast explosion. One British captain, describing the scene, wrote that, after the explosion "an awful pause and a death-like silence for about three minutes ensued, when the wreck of the masts, yards, etc., which had been carried to a vast height, fell down into the water, and on board the surrounding ships".

Now the archaeological evidence shows that there were in fact two explosions on L'Orient - one at the bow and one at the stern. The archaeological team has even located the 75ft central portion of the vessel - but they also discovered twisted and wrecked cannons lying up to 250 yards apart, testimony to the brute force of the explosion. The warship blew up when fires on board reached the powder magazines - and archaeologists who have brought objects to the surface say they still smell of gunpowder.

The excavations, the culmination of three years of work, are also shedding light on the human tragedy - and on political aspects of the French defeat. The mud of the seabed has been yielding up tobacco pipes, shoes, metal boxes and swords. However, it is also giving up other secrets: hundreds of gold coins seized by Napoleon from the island of Malta, which prior to the seizure had been run by the ancient and extremely wealthy Knights of the Order of St John; and the lead typefaces from a printing press, presumably used by Napoleon and his staff to produce propaganda. Skeletons, too, are being brought to the surface - tragic reminders, 200 years on, of the human cost of the battle.

The team - of which the leader is the French archaeologist Franck Goddio, of the European Institute for Underwater Archaeology - has also found the 36ft, 15-ton rudder of L'Orient, inscribed with its pre-revolutionary name, Le Dauphin Royal - a case of the ghost of royalist France coming back to haunt Napoleon and the French republicans.

Before the archaeologists made their discovery off the coast of Egypt, one of the few surviving fragments of the French flagship was a length of the vessel's mast, which had been recovered from the surface of the sea by an eccentric British captain. He had turned it into a coffin and presented it to Nelson as a somewhat macabre present.

The captain thought that his hero would wish some day to be buried in the mast of his greatest foe's flagship - and thus it was that, eight years later, after Trafalgar, Nelson was interred in St Paul's Cathedral in that very coffin. Even Napoleon was probably impressed.