Amateur archaeologist Lucas Schmid toted his metal detector onto a small hill beside a river gorge near the mountain village of Tiefencastel, Switzerland, and began probing the turf where an ancient battle had taken place. He would soon discover a Roman dagger from under the earth, which would lead to a remarkable excavation. Rumor had it that a “lost” battle between the Romans and the Rhaetians had occurred here some 2,000 years ago—for archeological excavations in 2003 had yielded traces of an ancient Roman army nearby, most of which it was assumed had been collected. Schmidt had a hunch, though, that the area had not yet been meticulously picked clean of ancient artifacts. He began surveying the area in 2018; and one year later, in the spring of 2019, his metal detector picked up a faint signal on the hill that day. Assuming it was a small metal object at first, …