The leaflet looked innocuous at first sight but it contained a message designed to instil fear and loathing. I found it in my post box in the sleepy district where I live in Marseille, France's second- largest city. The leaflet featured two National Front representatives, though my neighbourhood has yet to see the far-right party gain a foothold. Their message was poisonous. Bizarrely accusing political rivals of secretly funding an underground mosque, they went on to claim that those who frequented the mosque had the long beards of Salafists, adherents to an ultra-conservative form of Islam. This, they added cynically, was raising concerns in, as they put it, "the post-Charlie context" - a reference to the deadly attack on the offices of satirical magazine 'Charlie Hebdo' earlier this year.
Across France, the National Front's argument that immigration is to blame for crime, unemployment and an over- burdened social welfare system is gaining ground. It claims its membership has grown after 17 people were killed in the attacks on 'Charlie Hebdo' and a kosher supermarket in Paris in January. Two months later, the National Front came second only to Nicolas Sarkozy's UMP in France's local elections, after coming first in the European parliament elections last year. This week its leader, Marine Le Pen, said it had gathered enough support from other MEPs to form a far-right political bloc in Brussels.
Here in Marseille, one of France's most diverse cities, the National Front has been making worrying inroads. While certain towns and villages in the surrounding region of Provence have long been National Front strongholds, cosmopolitan Marseille proved immune until relatively recently. Voters in the city's troubled northern districts caused shockwaves two years ago when they elected a National Front mayor who subsequently won a seat in the French senate. These electoral wins have prompted fears that the tolerance many in the city have long boasted about may be at risk.
It is estimated every fifth person living in Marseille was born abroad and around one in three residents is Muslim.
Most are from former French colonies, particularly in north Africa. When Algeria's team surged in the 2014 World Cup tournament, the streets of Marseille were filled with joyous supporters who trace their roots back to the country.
Marseille's relatively good record of fostering social cohesion has often been held up as something of a model for other large French cities, and indeed elsewhere in Europe. The riots that spread across the suburbs of Paris and Lyon in 2005 failed to ignite Marseille -testament, many here say, to its ability to practice coexistence better than anywhere else.
But others say that much-vaunted harmony is under pressure as never before in a city where some districts are blighted by rising youth unemployment and poverty.
The stakes are high. According to the OECD, Marseille is the most economically divided city in Europe. The wealthiest of its districts are in the south, where chic restaurants and galleries cater for newly transplanted Parisians drawn by efforts to reinvent Marseille as a buzzy hub where Europe meets the Maghreb.
But the city's restive northern flank is where most of the recently arrived immigrants, many of them Muslim, live. There, unemployment stands at more than 20pc - and some 40pc of teenagers have dropped out of school. French footballer Zinedine Zidane grew up in one particularly notorious housing estate, a flash of inspiration in an otherwise grim landscape scarred by the drugs trade. Another part of the sprawling district known to locals as les quartiers nords is home to the National Front mayor, voted in by predominantly older residents fearful of a changing Marseille.
The National Front in Marseille has spent years trying to scupper plans to build an official mosque in the city. Despite having one of France's largest Muslim populations, Marseille has no purpose-built mosque. Efforts by local Muslims to rectify this have dragged on for years, beset by legal challenges - including from the National Front - and funding shortfalls. While they wait for a house of worship to call their own, the city's estimated 300,000 Muslims make do with makeshift prayer houses in basements, warehouses and rented rooms. Some Muslims here fret that this is exactly the kind of environment where hardline Salafists can find a more receptive audience, particularly among the youth, allowing them to flourish.
Tens of thousands turned out in Marseille for the 'Je Suis Charlie' rallies in January. And the city's hugely popular football team - which locals sometimes quip is the only thing that truly unites them - donned black shirts as a mark of respect to those who died in Paris. Around the city graffiti and posters still pay homage to the magazine. But the mood is more fraught these days. Marseille, and France more generally, knows that testing times lie ahead.