In 1733, Voltaire met Émilie du Châtelet (Marquise du Châtelet), a mathematician and married mother of three, who was 12 years his junior and with whom he was to have an affair for 16 years. To avoid arrest after the publication of "Lettres", Voltaire took refuge at her husband's château at Cirey on the borders of Champagne and Lorraine. Voltaire paid for the building's renovation, and Émilie's husband sometimes stayed at the château with his wife and her lover. The intellectual paramours collected around 21,000 books, an enormous number for the time. Together, they studied these books and performed scientific experiments at Cirey, including an attempt to determine the nature of fire.