 Hippolytus further presents individual teachers such as Simon, Valentinus, Secundus, Ptolemy, Heracleon, Marcus and Colorbasus.Tertullian (c. 155–230) from Carthage wrote "Adversus Valentinianos" ('Against the Valentinians'), c.206, as well as five books around 207–208 chronicling and refuting the teachings of Marcion.Prior to the discovery at Nag Hammadi, a limited number of texts were available to students of Gnosticism.