Jean-Baptiste Le Rond d'Alembert was co-editor with Denis Diderot of the Encyclopédie and also made important discoveries in physics and mathematics. He was the illegitimate son of the writer Claudine Guérin de Tencin and a few days after his birth, his mother left him on the steps of the Church of Saint-Jean-le-Rond in Paris. According to custom, he was named after the patron saint of the church. D'Alembert was adopted by the family of an artisan and attended a private school. At age 12, he was admitted to the Collège Mazarin (now called Collège des Quatre-Nations), where he studied philosophy, law, and the arts. He then went to law school for two years and was certified as a lawyer, taking the surname d'Alembert. D'Alembert was also a Latin scholar of note and worked in the latter part of his life on a translation of Tacitus, from which he received wide praise, including that of Denis Diderot. In 1743, he published his most famous work, Traité de dynamique, in which he developed his own laws of motion. When the Encyclopédie was organized in the late 1740s, d'Alembert was engaged as co-editor for mathematics and sciences. He authored over a 1,000 articles for it, including the famous Preliminary Discourse. D'Alembert frequented several Parisian salons, particularly those of Madame Geoffrin, Madame du Deffand, and Julie de Lespinasse, his dear friend.