In 1488, at the age of 13, Michelangelo was apprenticed to Ghirlandaio.[14] The next year, his father persuaded Ghirlandaio to pay Michelangelo as an artist, which was rare for someone of fourteen.[15] When in 1489, Lorenzo de Medici, de facto ruler of Florence, asked Ghirlandaio for his two best pupils, Ghirlandaio sent Michelangelo and Francesco Granacci.[16] From 1490 to 1492, Michelangelo attended the Humanist academy which the Medici had founded along Neo-Platonic lines. At the academy, both Michelangelos outlook and his art were subject to the influence of many of the most prominent philosophers and writers of the day including Marsilio Ficino, Pico della Mirandola and Poliziano.[17] At this time, Michelangelo sculpted the reliefs Madonna of the Steps (1490–1492) and Battle of the Centaurs (1491–1492).[13] The latter was based on a theme suggested by Poliziano and was commissioned by Lorenzo de Medici.[18] Michelangelo worked for a time with the sculptor Bertoldo di Giovanni. When he was seventeen, another pupil, Pietro Torrigiano, struck him on the nose, causing the disfigurement which is conspicuous in all the portraits of Michelangelo.[19]