A 250-year-old book by the Enlightenment anti-establishment writer Voltaire is climbing best-seller lists in France weeks after attacks by French-born Islamic extremists that left 20 people dead, including the gunmen.

The "Treatise on Tolerance" is a cry against religious fanaticism and stemmed from Voltaire's conviction that religious differences were at the heart of world strife. He wrote at a time of bloody tension between French Protestants and Catholics.

The Jan. 7-9 attacks started when two gunmen stormed Charlie Hebdo, a satirical weekly that had received death threats for caricatures of the Prophet Muhammad, decimating the paper's staff. Also attacked was a kosher supermarket, where four hostages died. The attack on Charlie Hebdo was widely seen in France as an attack on freedom of expression and the secular state, and in the days after Voltaire's writings were frequently invoked. Several bookstores in Paris are giving the Enlightenment philosopher prominent display space.