The oval-shaped stone age fort at Čiudiškiai

The Čiudiškiai hillfort, dating back six thousand years to the first half of the 1st century AD, is older than the Pyramids. It sits in a separate valley on the right bank of the Morkūna River slope, in Išlaužo seniūnija, Prienų rajono savivaldybės teritorijoje. The oval-shaped hillfort, with entrances on the right and left sides, is sixty metres long and twenty-six metres wide. Its walls are three to nine metres high, built from stone and earth. The hillfort, covering an area of five thousand eight hundred square metres, was built by Stone Age people and its roofed structures remain at the site, covering an area of three hundred square metres.

Sources: Wikipedia, OpenStreetMap, Wikidata, Wikimedia Commons