MEGAN THOMPSON:

This city of more than 850,000 is France's second largest and one of its most diverse. About 500 miles southeast of Paris and on the Mediterranean, Marseille is home to tens of thousands of immigrants throughout Europe and more recently from North Africa.

By some estimates, the city is now 30 to 40 percent Muslim, one of the highest concentrations of Muslims anywhere in this overwhelmingly Catholic country. Even before yesterday's attack and even before two other recent attacks in France by Muslim men, tensions in Marseille between Muslims and non-Muslims had been rising.