 The Arabic tradition is another important source of information about Simplicius (for a concise summary, see Goulet &amp; Coda 2016: 384–394; see also Vallat 2014a and 2014b and Gätje 1982). As in the Latin tradition, the Commentaries on the Categories and the De anima seem to have primarily been read by scholars (in both Arabic and Syriac). However, there also appears to be some evidence for a lost Commentary on the First Book of Euclid (Goulet &amp; Coda 2016: 390–394; I. Hadot 2014, 39–53; R. Rashed 2005). Before Simplicius, Proclus had already commented on Euclid. Proclus’ commentary still exists, and so there is a question regarding Simplicius’ motivation for writing a second commentary, and it may be that Simplicius’ commentary was simply an augmented and revised version of Proclus’ commentary. Philosophers in the Arabic tradition, like those in the Latin tradition, also used Simplicius to defend the harmony of Plato and Aristotle.