The History of the Decline and Fall of the Roman Empire Volume I by Edward Gibbon

Although decline is the theme of this massive work, the Roman military machine shows itself still quite capable of defeating its enemies when competently led, and there is no shortage of outstanding emperors in this period. Special praise is reserved for Constantine, the great Christianizer and victorious general, and surprisingly, his antithesis, Julian the pagan restorationist who was equally successful on the battlefield. The decline seems to be in the morals of the populace rather than in the strength of the empire, and from this book alone it is not easy to see why the empire should have eventually fallen. The book ends with an ominous and uneasy truce with the Goths under the emperor Theodosius, with the implication that the presence of the Goths within the empire will be its ruin, but even this does not seem to have been inevitable. Why did the Roman Empire fall? Perhaps, as Victor Hugo said of the reign of Napoleon, God grew bored with it.