Pappus wrote a Commentary on Euclid's Elements, but except for some small fragments all that survives is an Arabic translation of commentary on book 10. This provides an English translation. What Pappus says about Euclid's math is not nearly as interesting as how he places Euclid in relationship to three of his predecessors: Theaetetus, Pythagoras and Aristotle. It is fascinating to see how Pappus harmonizes Euclid with two of Plato's works, Parmenides and Theaetetus, without ever admitting in writing that Plato was wrong mathematically.