Were it not for the placards, anyone strolling past the National Gallery might have thought the gathering was a novel extension to the debutante season.
In fact, the movers and shakers of young London society were attending Britain's poshest demonstration. Fred Lambton, the 22-year-old heir to the earldom of Durham, was there. So too were other aristocrats and scions of the internationally wealthy.
Their irritation, expressed in occasional chants during a three-hour rally on Saturday, was directed at the sponsor of an exhibition in the gallery's Sainsbury wing. Their cause: the protection of the Tuscan countryside.
An Italian bank sponsoring the show of Renaissance art from Siena is also one of the main financiers of a plan to develop a small aerodrome outside the walled city into an international airport handling 500,000 passengers a year.
One of its directors is Prince Girolamo Strozzi, who provided Tony Blair and his family with free summer holidays at his 16th-century palace.
The Save Siena Campaign enjoys support from Joseph Getty, son of the billionaire Sir Paul Getty, the polar explorer Arthur Jeffes, and the Guinness and Hesketh families. Marissa Montgomery, who founded the Pussy Glamore lingerie chain, is another supporter.
Many have personal links to Tuscany – nicknamed Chiantishire because of its popularity with the English – having spent holidays at second homes in the region. They fear that turning Siena's tiny airfield into an international airport will shatter the peace of rural Tuscany and present many other problems, from water shortages to noise.
Lambton, a grandson of the former Tory minister Lord Lambton, denied that the protesters were trying to prevent holidaymakers on no-frills airlines from blemishing Siena.
He said: "Every summer Siena gets saturated with tourists. Building an airport isn't going to add tourists because it's already flooded with tourists."
Rather, he claimed, the airport would ruin the character of the city and destroy its beauty and tranquility.
Halting the project would also prevent any further damage caused by climate change, added Lambton, the stepson of the television presenter Jools Holland.