Library 422NPNF2-01. Eusebius Pamphilius: Church History, Life of Constantine, Oration in Praise of Constantine
That opens the app in your browser. A first visit installs about 15 MB before anything else; this book is its own download, and you can keep it offline or take it back off whenever you like. Out of copyright, from the Christian Classics Ethereal Library (CCEL) edition.