After living in their 18th-century United Kingdom townhouse for ten years, an anonymous couple decided it was time to make a few upgrades. During the renovations, however, they unearthed the surprise of a lifetime: more than 260 rare gold coins dating back hundreds of years, reports CNN’s Sana Noor Haq.

And while it’s unclear how much the couple spent on their home improvement project, the coins may just help offset some of the costs. They’re expected to fetch upwards of £250,000 ($288,000) at auction next month, per an emailed statement from the auction house Spink & Son.

The couple found the coins in July 2019 while renovating their home in Ellerby, a village in North Yorkshire in the northeastern part of England. As they worked to replace the home’s kitchen floor, the couple encountered what they initially thought was an electrical cable buried beneath the concrete.

But when they investigated the obstruction, they realized they’d hit upon a small stoneware cup brimming with gold coins. The cup, buried six to eight inches below ground, was about the same size as a soda can, per Spink & Son.

“The remarkable trove is unlike any find in British archaeology or like any coin auction in living memory,” says Gregory Edmund, a numismatist with Spink & Son, in an emailed statement.

Though the discovery is rare, the money pieces themselves would’ve been used as ordinary, everyday coins during their day.

The coins date to between 1610 and 1727, and were originally worth somewhere in the range of £50 ($57) to £100 ($115).

The rarest and most valuable of all the coins is a misprinted George I guinea from 1720 that features two “tails” sides. The auction house estimates it to be worth around £4,000 ($4,600). Another rare misprint, a Charles II guinea that misspells his Latin name, is worth around £1,500 ($1,725).

Fortunately, the coins do not meet the specifications for “treasure” under British law, which means the couple got to keep most of them, reports ArtNet’s Sarah Cascone.

After some legal back and forth, a coroner with the British government ultimately decided that the coins could be disclaimed because the youngest—a George I guinea from 1727—was less than 300 years old at the time of the discovery, per Spink & Son. The government plans to keep just one artifact—a rare Brazilian gold coin that circulated in England in the 1720s—and will add it to the collection of one of its museums.

Before the fortuitous discovery, the coins likely belonged to Joseph and Sarah Fernley-Maisters, a married couple that came from a prosperous mercantile family that made money trading in natural resources like timber, coal and iron ore. They were married in 1694; Joseph Fernley-Maisters died in 1725, and Sarah Fernley-Maisters died in 1745.

Based on their decision to stash the money underground, the couple “clearly distrusted the newly-formed Bank of England, the ‘banknote’ and even the gold coinage of their day because they [chose] to hold onto so many coins dating to the English Civil War and beforehand,” says Edmund in the statement.

“Why they never recovered the coins when they were really easy to find just beneath original 18th-century floorboards is an even bigger mystery, but it is one hell of a piggy bank,” he says.