Gibbon Chapter XLVI: The Persians, the Avars and Heraclius
This is one of the best chapters we have had for ages - I found myself marking almost every page with some point of interest. Gibbon describes the fatal interaction of the Byzantine and Persian empires in the early seventh century - close personal bonds between the respective emperors, which none the less deteriorate into dreadful combat and slaughter, with each empire's armies penetrating deep into the other's territory, to the point that both capitals were seriously threatened at different stages. We also have the Avars coming down the other side of the Black Sea to hit the Byzantines from the northwest. Gibbon seems really energised by it, and of course we end in the 620s, when events which would prove far more significant in terms of world history were unfolding a little to the south.