Gabrielle-Émilie Le Tonnelier de Breteuil (known as Emilie), considered one of the great beauties of the early 18th-century, was born in Paris to a family of the lesser French nobility. She received an unusually rigorous education for a girl of her time, being taught Latin, Italian, Greek, German, mathematics, literature, and science, as well as gymnastics and riding. In 1725, at age 18, she was married to Florent-Claude du Chastellet-Lomont, marquis du Chastellet, 10 years her senior. The spelling "Châtelet" was introduced by Voltaire later and has now become standard. She and her husband had three children, but lived independent lives. Madame du Châtelet's accomplishments included writing poetry, solving math problems, and conducting physics and chemistry experiments. Her most famous achievement was her translation into French, with her own commentary on the conservation of energy, of Isaac Newton’s great work Principia Mathematica, thus furthering French science. Madame du Châtelet and Voltaire became lovers and long-time companions. He fled Paris under threat of arrest and took refuge with her at her château of Cirey in Champagne. There they worked togther on their scientific and philosophical projects. After their relationship waned, she became pregnant by another lover and died at age 43 shortly after giving birth to a daughter.