... Did the Celts see a comet impact in 200 B.C. ? A new-found field of impact craters may mark the site of a recent comet strike. The Chiemgau Impact Research Team . ... Chiemgau . ... This pushes the earliest date for the impact to the late Celtic period, between 480 b.c. and 30 b.c. Radiocarbon dates from ash samples we removed from layers in several craters are not yet available. ... On the rim of the largest crater, named TУМttensee, archaeologists have found Roman relics from about a.d. 200. ...