Proclus' Commentary on Plato's dialogue Timaeus is arguably the most important commentary on a text of Plato, offering unparalleled insights into eight centuries of Platonic interpretation. This edition offers the first new English translation of the work for nearly two centuries, building on significant recent advances in scholarship on Neoplatonic commentators. It provides an invaluable record of early interpretations of Plato's dialogue, while also presenting Proclus' own views on the meaning and significance of Platonic philosophy. The present volume, the first in the edition, deals with what may be seen as the prefatory material of the Timaeus. In it Socrates gives a summary of the political arrangements favoured in the Republic, and Critias tells the story of how news of the defeat of Atlantis by ancient Athens had been brought back to Greece from Egypt by the poet and politician Solon.