Diligence and accuracy are the only merits which an historical writer may ascribe to himself; if any merit, indeed, can be assumed from the performance of an indispensable duty. I may therefore be allowed to say, that I have carefully examined all the original materials that could illustrate the subject which I had undertaken to treat. Should I ever complete the extensive design which has been sketched out in the Preface, I might perhaps conclude it with a critical account of the authors consulted during the progress of the whole work; and however such an attempt might incur the censure of ostentation, I am persuaded that it would be susceptible of entertainment, as well as information. At present I shall content myself with a single observation. The biographers, who, under the reigns of Diocletian and Constantine, composed, or rather compiled, the lives of the Emperors, from Hadrian to the sons of Carus, are usually mentioned under the names of Ælius Spartianus, Julius Capitolinus, Ælius Lampridius, Vulcatius Gallicanus, Trebellius Pollio and Flavius Vopiscus. But there is so much perplexity in the titles of the MSS., and so many disputes have arisen among the critics (see Fabricius, Biblioth. Latin. l. iii. c. 6) concerning their number, their names, and their respective property, that for the most part I have quoted them without distinction, under the general and well-known title of the Augustan History. Preface To The Fourth Volume Of The Original Quarto Edition. I now discharge my promise, and complete my design, of writing the History of the Decline and Fall of the Roman Empire, both in the West and the East. The whole period extends from the age of Trajan and the Antonines, to the taking of Constantinople by Mahomet the Second; and includes a review of the Crusades, and the state of Rome during the