Start your weekend with a bang this Thursday evening at 6pm

How do you celebrate something as multifaceted as the City of London? It is a place of contradictions: both a glass-fronted metropolis and a cluster of stone relics, stubborn and robust. It throngs with people of all nationalities and hums with activity that is at once local and global.

Crammed into a single square mile (marginally bigger, if we’re being precise) are around 300,000 workers and hundreds of heritage sites, architectural icons old and new, public sculptures and statues, organisations, associations and cultural bodies. All because, some 2,000 years ago, some Roman set down his stall on the bank of the Thames.

Celebrate the City aims to cover all that and more, squeezing everything the Square Mile offers into the long weekend that straddles midsummer (21-24 June). “The City has an enormous amount of culture going on every day,” explains Sir Nicholas Kenyon, Managing Director of the Barbican Centre, “but in this special year of 2012, we wanted to draw it all together over four days.”

In fact, organisers hope to go one better and condense the spirit of the City into a single launch event.

On Thursday evening, at 6pm, Celebrate the City begins with a bang. Sixteen of them in fact; each a cannon shot in Tchaikovsky’s iconic 1812 Overture performed outdoors in Guildhall Yard by students from Guildhall School of Music & Drama. Admission is free.

Guildhall Yard makes perfect sense as a launch pad. It’s bang in the centre of the City and embodies 2,000 years of the City’s history and architecture. From it you can see a paved circle on the floor that marks the Roman amphitheatre preserved underneath and the Guildhall itself, which dates back to the 15th Century and mixes gothic and modernist architecture. On the south side stands St Lawrence Jewry, designed by Christopher Wren in the 17th century and rebuilt after the Second World War, and on the east side is Richard Gilbert Scott’s Guildhall Art Gallery, a relative fledgling at only 13 years old.

Project Director, Stella Ioannou, believes the Yard is one of London’s hidden treasures. “You can talk to someone who works in a business next door, and they might never have been into the yard. That’s what Celebrate the City is all about: a magnificent public space, a big musical performance and, hopefully, some sunshine.”

The Lord Mayor suggested the 1812 Overture as a personal favourite – and, of course as a resounding and triumphant piece of music which captures perfectly the celebratory mood of this event.

As a favourite of Independence Day celebrations, many Americans think it recalls the USA’s defeat of the British Empire. However, Tchaikovsky was actually writing about Russia’s victory over Napoleon’s French in the same year.

Nonetheless, Napoleonic Wars hardly scream London. Fortunately Jonathan Dove’s River Songs, which opens the event, does. The cantata is inspired by the River Thames.

It will be performed by a selection of choirs, several made up of employees at major City companies including Standard Chartered and Hearst Magazines. Brought together by Music in Offices, a charity run by Tessa Marchington and Guildhall graduate Joel Garthwaite, they will sing alongside the Guildhall Staff Chorus and choirs from Barbican School and BBC Worldwide Service, building to a ten minute crescendo featuring hundreds of combined voices – just over 250 of them.

“Audiences’ relationships to heritage and culture are really changing,” says Kenyon. “Rather than being passive observers, they really want to take part and have a sense of ownership.

When a piece of music is as rousing as Tchaikovsky’s though, most are happy to sit back and be blown away.”

The 1812 takes its time to build. A slow and solemn start grows into a series of running battles between brass and string sections. Fragments of the Marseillaise compete with Russian folksongs. First the French seem to be winning, then the Russians. It teases you with morsels of that familiar final refrain (do-do-do-do-do-do-do-bom-bom) before soaring into its final jubilant cacophony of cannon fire and clanging bells. It’s an explosive 16 minutes.

“It’s the perfect piece for this sort of occasion,” says Kenyon, “It’s perfect for the outdoors. If it were any longer, you’d want to sit down. Everybody knows some of it and it will make a huge impact.”