Last year a metal detectorist working in a field near Swaffham, Norfolk, England, found this spectacular Anglo-Saxon brooch. It's made of silver inlaid with niello, a black alloy, 2 inches (5 cm) across, probably from the 9th century.
Archaeologists were sent to the site; digging down, they found a nineteenth-century plow. So the knew that the brooch was in fill brought from somewhere else. At this point someone thought to ask the farmer (a different person from the landowner) and he said that, yes, it was fill, but he didn't know where it came from because he had just "flagged down a passing truck."
So a great mystery: where did the soil come from, and were there other wonders that maybe got shipped off in other truckloads of topsoil to other nearby spots? I wonder if Norfolk residents who had fill put down on their property over the past few years are all out checking it with metal detectors.