... it was almost a year ago! I think it was the beginning of my sabbatical month last year, which I'm trying desperately not to do this year, despite being absent a lot!

Oh well, here is the rest of the answer: it's the final part of Das Grab im Busento, indeed by August von Platen, about the burial of Alaric in the river Busento (near Cosenza, Italy) in 410, just after the Visigoths' sacking of Rome. Italian poet Giosue Carducci translated it in his poem La tomba nel Busento.