To the best of my knowledge, nothing like this ever happened. Admittedly, there are many gaps - some yawning, some narrow but deep - in the long narrative of Roman history. But I'm reasonably confident that a rogue leopard mauling an emperor's son would not have slipped through the cracks.

The Parthians sometimes sent exotic animals as diplomatic gifts; Pacorus II, for example, dispatched lions and ostriches (hopefully in separate crates) to the Chinese emperor. The Parthians (and later, Sassanians) occasionally sent tribute, hostages, and/or gifts to Roman emperors - one thinks of the famous legionary eagles recovered by Augustus - but not lions or leopards. The Romans themselves, after all, were not exactly strangers to big cats, having a remarkably sophisticated system for capturing the lions and other toothy critters found within their own domains.

(I feel compelled to note, more or less parenthetically, that there were maulings in Rome, and not just in the Colosseum; before major games, big cats and other predators were kept in primitive zoos, whose security was less than airtight; "how often," laments Tertullian, "have wild beasts broken from their cages and devoured men in the middle of cities?")

The sons of Roman emperors were not immune to the grim demographic realities of the premodern era. Many died of childhood diseases - of the 14 children of Marcus Aurelius, for example, only 5 survived to adulthood - and others succumbed to dynastic politics (like Geta, murdered by his brother Caracalla) or on the battlefield (like Herennius Etruscus, killed with his father at the disastrous battle of Abritus). Yet none of them, so far as our Greek and Roman sources report, was felled by a leopard.