Can't speak as to this specific find, but it was common for slaves to be condemned to work in the mills or bakeries as a punishment. We don't think of such things as gruesome today, but, well...

When the day was mostly past, and I was weary, they un-harnessed me, removed my collar, and tied me to the manger. Though I was utterly exhausted, urgently in need of restoring my strength, and almost dead from hunger, still my usual sense of curiosity kept me upright with its nagging: I neglected the pile of fodder, and was pleased to watch the life of that detestable mill.

You blessed gods, what a pack of dwarves those workers were, their skins striped with livid welts, their seamed backs half-visible through the ragged shirts they wore; some with loin-cloths but all revealing their bodies under their clothes; foreheads branded, heads half-shaved, and feet chained together. They were wretchedly sallow too, their eyes so bleary from the scorching heat of that smoke-filled darkness, they could barely see, and like wrestlers sprinkled with dust before a fight, they were coarsely whitened with floury ash.

While the description here is from a satirical work, it is contemporary (The Golden Ass, 2nd century AD) and can be judged to be accurate in broad strokes, even written with dramatic flair in a fictional adventure.