Under a soccer field in a Vienna neighborhood along the Danube, archaeologists have found a mass grave dating to the era when the Roman Empire was battling Germanic tribes almost 2,000 years ago, experts announced this week. The grave was discovered in October by a construction company doing renovations for the field in Vienna’s Simmering district, a team of archaeologists and historians at the Vienna Museum said in announcing its findings. The extraordinary discovery was tied to what they called a “catastrophic” military event, possibly one where Roman troops were badly defeated and fled the site quickly. Radiocarbon dating traced the bones to approximately A.D. 80 to 234 — a period in which more than a dozen Roman emperors ruled, including Domitian and Trajan, who clashed with ancient Germanic people in the region. An analysis of other items found in the grave, including an iron dagger, lance points, scale armor and a cheek piece of a helmet, helped confirm the time period. Near the foot of one skeleton, the archaeologists also discovered shoe nails that came from distinctive Roman military shoes called caligae.