In the French Alpine town of Saint-Genis-Pouilly, seething Muslims demanded that a municipal center cancel a play by Voltaire—but instead of submitting, the mayor called out the police: Muslims ask French to cancel 1741 play by Voltaire.

A municipal cultural center here on France’s border with Switzerland organized a reading of a 265-year-old play by Voltaire, whose writings helped lay the foundations of modern Europe’s commitment to secularism. The play, “Fanaticism, or Mahomet the Prophet,” uses the founder of Islam to lampoon all forms of religious frenzy and intolerance.

The production quickly stirred up passions that echoed the cartoon uproar. “This play … constitutes an insult to the entire Muslim community,” said a letter to the mayor of Saint-Genis-Pouilly, signed by Said Akhrouf, a French-born cafe owner of Moroccan descent and three other Islamic activists representing Muslim associations. They demanded the performance be cancelled.

Instead, Mayor Hubert Bertrand called in police reinforcements to protect the theater. On the night of the December reading, a small riot broke out involving several dozen people and youths who set fire to a car and garbage cans. It was “the most excitement we’ve ever had down here,” says the socialist mayor.

The dispute rumbles on, playing into a wider debate over faith and free-speech. Supporters of Europe’s secular values have rushed to embrace Voltaire as their standard-bearer. France’s national library last week opened an exhibition dedicated to the writer and other Enlightenment thinkers. It features a police file started in 1748 on Voltaire, highlighting efforts by authorities to muzzle him. “Spirit of the Enlightenment, are you there?” asked a headline Saturday in Le Figaro, a French daily newspaper.