(Newser) – Laurence Egerton's metal-detecting excursions often resulted in such "treasures" as old shotgun cartridges and other "rubbish," he says. But last November, the UK builder found something much better—22,000 fourth-century Roman coins, the biggest such cache ever found in Britain. The coins, which date from AD260 to AD348 and are known as the Seaton Down Hoard because of where they were found, went on temporary display at the British Museum last week, the Telegraph reports. But before that, they had to be excavated—and while archaeologists worked on that, Egerton, 51, couldn't bring himself to leave the site. "I slept in my car alongside it for three nights to guard it," he says. "Every night the archaeologists packed up and left, and I couldn’t go home and sleep thinking there was something of such significance sitting there in a hole in the ground." Experts are impressed with the find, which includes coins struck in honor of the foundation of Constantinople in AD332 that feature Emperor Constantine the Great's image; one archaeologist says they were probably someone's savings.

"There were no High Street banks, so a good, deep hole in the ground was as secure a place as any to hide your savings in times of trouble, or if you were going away on a long journey," he explains. They were found in a field near a previously excavated Roman villa site, and Egerton first spotted two thumbnail-sized coins on the ground. His metal detector then uncovered iron underground—something many metal detectors won't do, because it's typically worthless—and he soon found himself bringing up a "shovel ... full of coins—they just spilled out over the field," he says. Authorities declared the coins to be official treasure, meaning they're eligible to be acquired by a museum; the Royal Albert Memorial Museum is trying to raise the money to buy them. Egerton has a license to operate on the land where they were found, so he and the landowner will split the proceeds—and the copper coins could be worth tens of thousands of dollars, though in their day, an expert tells the Guardian, they were probably only worth the equivalent of four gold coins. Egerton hopes to keep one of the coins as a memento. "I have found lots of interesting items but never anything of this magnitude," he says. "It really doesn't get any better than this." (This summer, an artist hid $16,000 worth of gold bars on a beach.)

