"The bond between our countries and our citizens is indestructible," Macron said after the two men lunched at the Clos Luce, the sumptuous manor house where Leonardo spent the last three years of his life.

Mattarella and Macron, who was accompanied by his wife Brigitte, began their visit at the royal chateau in Amboise, where the heads of state laid wreaths at Leonardo's grave.

The Italian leader had started his day with a visit to the fire-ravaged Notre Dame cathedral in Paris.

The joint celebrations come after months of mounting diplomatic tensions between Paris and Rome over the hardline policies of Italy's populist government and its support for France's anti-government "yellow vest" protesters. 

In the worst diplomatic crisis between the two countries since World War II, Paris briefly recalled its ambassador from Rome.

Amboise, a sleepy town on the Loire River where Leonardo died in 1519 aged 67, was in virtual lockdown because of fears of protests by France's grassroots "yellow vest" movement.

Amboise was turned into a ghost town, with traffic banned within a five-kilometer radius and the usually teeming restaurants and shops shuttered. On Wednesday, dozens of cars were towed away, with some foreign owners apparently unaware of the draconian security measures in the town of just 13,000.

The presidential helicopter arrived on a river island in the heart of the town, touching down on a pad usually used to launch hot-air balloons over the chateau-studded valley.

Also Thursday, the two presidents visited the sprawling chateau of Chambord -- whose central double-helix staircase is attributed to Leonardo though the first stone was not laid until four months after his death.

Among glitterati attending the events were Italian star architect Renzo Piano, French astronaut Thomas Pesquet and historian Stephane Bern, a prominent French television personality.

At Chambord, Pesquet told a group of around 500 Italian and French youths: "If Leonardo were alive today, maybe he would be a European astronaut."

The entire Loire Valley has seized on Leonardo's quincentenary as that of the Renaissance in general, planning more than 500 events across the region, with Bern as the figurehead.

Read also: At Amboise, Leonardo's last years paint a picture of Franco-Italian harmony

'Architect of the king'

Francis I, known as the "Sun King of the 16th century", is widely credited with bringing the Renaissance to France, even if his predecessor Louis XII had begun the process by bringing in architects and artisans from Florence, Milan and Rome.

Leonardo was 64 when he accepted the young Francis I's invitation to Amboise, at a time when rivals Michelangelo and Raphael were rising stars.

With Leonardo's commissions drying up, it came as a great relief and no small vindication for the Tuscan artist, who received a handsome stipend as the "first painter, engineer and architect of the king".

At the time, Francis I was barely 23, and his ambitious mother Louise of Savoy "knew that Leonardo would be the man who would allow her son to flourish", Catherine Simon Marion, managing director of the Clos Luce, told AFP. 

Leonardo brought with him three of his favorite paintings: the Mona Lisa, the Virgin and Child with Saint Anne, and Saint John the Baptist -- all of which today hang in the Louvre museum in Paris.

Italy and France have also sparred over an accord under which Italy will lend several Leonardos to the Louvre in October.

With fewer than 20 Leonardo paintings still in existence, many Italians are resentful that the Louvre possesses five of them, as well as 22 drawings. 

During his three years in Amboise, Leonardo organised lavish parties for the court and worked to design an ideal city for Francis at nearby Romorantin -- one of the polymath's many unrealized projects -- all while continuing his research.