Construction workers building a new boathouse along the Rhine River in Switzerland have unearthed what is believed to be the ruins of a Roman-era amphitheater.
Archeologists believe the small, oval-shaped amphitheater dates to the 4th century based on a number of clues at the site, including the discovery of a coin dated between 337 and 341 A.D.
The stone blocks and mortar at the site also point to the 4th century since they are the type of building materials used for a fort wall in that era, archeologist Jakob Baerlocher, head of excavations in Kaiseraugst, Switzerland, told Live Science.
Kaiseraugst sits along the Rhine River near the borders of both France and Germany. The area is known as the Augusta Raurica garrison at the northern border of the Roman Empire.
This is the eighth ancient Roman amphitheater found in Switzerland, and it is believed to be the youngest of the group.
Its discovery came as a surprise to archeologists, who knew of a quarry at the location but were unaware an amphitheater would be sitting there as well.
“[The amphitheater] is located in the hollow of a quarry that was abandoned in Roman times, immediately west of Kaiseraugst Castle, the Castrum Rauracense,” the Department of Education, Culture and Sport said in a statement.
While more famous venues like the Colosseum in Rome could hold up to 50,000 spectators, most were much smaller. This new discovery measures just 164 by 131 feet, less than half the size of a football field.
Archeologists discovered a large gate to the south of the complex flanked by two side entrances. A threshold made from sandstone blocks was still preserved.
Another entrance was found on the west side with another sandstone threshold.
Wooden grandstands and a plastered arena wall are also part of the discovery.
“All the evidence together, the oval, the entrances, and the post placement for a tribune, lend credence to it being an amphitheater,” the statement said.
Historians believe the amphitheater was used for gladiator fights and animal hunts, popular events during Roman times.
The construction crew and the archeologists will now work together to both complete the boathouse project and preserve the amphitheater.
“Thanks to the close and good cooperation with the client, the construction project could be adapted in such a way that the Kaiseraugst amphitheater was preserved in the ground,” the statement said.
Officials noted the archeological substance is protected by a dam and the new building will be erected above it.
“The monument thus remains in its original place and is optimally protected so that it is preserved for the future,” the statement concluded.
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