The setting is a museum (or gallery, or library) in which the busts of a number of Roman Emperors are displayed. Although the speaker might (as Oxford suggests) be ‘a guide to some of the antiquities of Rome’, there is no warrant for this in the text. ‘Protus’ and his usurping successor ‘John the Pannonian’ are fictional, and, as Oxford remarks, ‘So far as chronology is concerned, Browning has deliberately muddied his tracks’. Protus is born ‘at Byzant’ (l. 10), i.e. Byzantium, the seat of the ‘Eastern Empire’, which from the end of the fourth century was ruled separately from the ‘Western Empire’, based in Rome. But although the Eastern Empire was forced to pay tribute to the Huns in the fifth century (l. 40), it was not conquered and enjoyed comparative stability; the events described in the poem seem more characteristic of the last period of the Western Empire, esp., as Ohio points out, the overthrow of the boy emperor Romulus Augustus (nicknamed ‘Augustulus’, i.e. ‘little Augustus’) by Odoacer: ‘In the year 475, by one of the endless revolutions which marked the close of the Western empire, the emperor Nepos was driven into exile, and the successful rebel Orestes was enabled to array in the purple his son, a handsome boy of fourteen or fifteen, who was named Romulus after his grandfather, and nicknamed Augustulus, from his inability to play the part of the great Augustus. Before this puppet emperor had been a year on the throne the barbarian mercenaries, who were chiefly drawn from the Danubian tribes before mentioned, rose in mutiny, demanding to be made proprietors of one-third of the soil of Italy. To this request Orestes returned a peremptory negative. Odoacer now offered his fellow-soldiers to obtain for them all that they desired if they would seat him on the throne. On the 23rd of August 476 he was proclaimed king; five days later Orestes was made prisoner at Placentia and beheaded; and on the 4th of September his brother Paulus was defeated and slain near Ravenna. Rome at once accepted the new ruler. Augustulus was compelled to descend from the throne, but his life was spared’ (EB). Note, however, that the Protus of B.’s poem is not a ‘puppet’ in this sense but a legitimate descendant of the imperial line (see l. 10). Moreover, there are precedents for the figure of the low-born but competent usurper from earlier periods of Roman history, e.g. the Emperor Aurelian (c. ad 215-75) who like ‘John the Pannonian’ fought against barbarian invaders (the Vandals), ruled for six years (270-5), and was murdered (near Byzantium).