The precise date of Spinoza's first studies of Latin with Francis van den Enden (Franciscus van den Enden) is not known. Some state it began as early as 1654–1655, when Spinoza was 20; others note that the documentary record only attests to his presence in van den Enden's circle around 1657–1658. Van den Enden was a notorious free thinker, former Jesuit, and radical democrat who likely introduced Spinoza to scholastic and modern philosophy, including that of Descartes. (A decade later, in the early 1660s, Van den Enden was considered to be a Cartesian and atheist, and his books were put on the Catholic Index of Banned Books.)