Construction excavators in Japan stumbled onto a huge treasure recently, unearthing an estimated 100,000 coins from a site outside Tokyo.

So far, the oldest coin dates to about 175 BC. The coins were consolidated into 1,060 bundles of about 100 pieces.

According to The Asahi Shimbun, the burial was likely intentional. They emerged from a small area, about 60 centimeters wide by a meter long, along with fragments of straw that suggested bundling. The newest coin so far dates to about 1265 AD — a fraught period of factional war in feudal Japan.

If that coin was contemporary at the time of burial, it would have existed as currency during the Kamakura Period (1185-1333). The period takes its name from a shogunate, or military government, that warred with the imperial administration throughout its existence. Multiple attempted Mongol attacks occurred in the 1270s and 1280s, which further stressed the regime.

Historians generally credit this coin hoarding behavior — which also occurred elsewhere in Japan around the same time period — to security efforts.

“The hoards may have functioned as a bank. Another theory is that hoarding had a symbolic meaning, possibly religious,” William Farris, a professor emeritus of Japanese history at the University of Hawaii at Mānoa, told Live Science. “I favor the theory that the coins were a type of bank for safekeeping.”

The Asahi Shimbun noted that the coins were found near the houses of “important” people in medieval Japan, suggesting a burial for safekeeping “because war was in the air.”

The City of Maebashi has displayed some of the coins in the lobby of its cultural protection division. Theories about the trove could change as expert investigation continues.