Complex sentence: The history, which had an apologetic aim, is no longer extant, but copious extracts from it are to be found in the "Chronicon" of Eusebius, who used it extensively in compiling the early episcopal lists.
Split into simpler sentences: The history, which had an apologetic aim, is no longer extant. But copious extracts from it are to be found in the "Chronicon" of Eusebius, who used it extensively in compiling the early episcopal lists.