Moscow-Asteady stream of devout Muslims pours into the Sobornaya Mosque on a cold, grey Friday afternoon. The Arabic call to prayer echoes incongruously among Soviet-era apartment buildings and monolithic relics of Moscow's 1980 Olympics. As usual, the mosque's blue walls cannot contain the hundreds of people looking to pray. "I'm sorry, it's full," a bearded man in a white skullcap repeats again and again to worshippers showing up at the doors.

Soon, the courtyard outside the mosque is crammed with men removing their hats and shoes to pray. Some lay down elaborate prayer mats of finely woven silk; others settle for tattered newspapers. When the men kneel in the direction of Mecca, their foreheads press against hard concrete. Attending the prayers with his 8-year-old son, Zabir Valeev can hardly hide his frustration at having to pray under these conditions. The two come to the Sobornaya Mosque nearly every Friday and are often forced to pray outside. "We shouldn't have to stand out here in the cold," says Valeev, 32. "What does it show to my son that there is no place in Moscow for us to pray?"

The Sobornaya Mosque is one of only four mosques in Moscow serving a Muslim population of 2.5 million — the largest of any European city. Crammed amid the grey monoliths of Moscow's 1980 Olympics complex, it was the only Islamic house of worship allowed to function during the Soviet period, usually empty due to religious repression.