The Kumelionių Hillfort, with its ancient settlement, is located in the Marijampolė Municipality, just 1.5 kilometers south of the village of Kumelionių, in the Marijampolė Rural Elderate, on the left bank of the Šešupė River. The hillfort is surrounded by nature—on the south and east it is bordered by the Šešupė River and its valley gullies, while the north side is defined by the deep Uosupėlis Valley. The slopes are very steep, reaching heights of 15-16 meters. The hillfort's plateau is elongated, measuring 38 by 6.5 meters, though part of it has slid into the Šešupė River. An ancient settlement was discovered at the western foot of the hillfort, covering an area of 150 by 200 meters. It was separated from the hillfort by a 45-meter-long and 3-meter-high rampart and a 2-meter-deep, 6-meter-wide ditch.
Exploratory archaeological surveys of the hillfort and settlement were conducted in 1968 by
a team of archaeologists from the Scientific Methodological Council for the Protection of Cultural Monuments, led by Vytautas Daugudis. They investigated a 48 square meter area of the plateau and a 5 by 25 meter section of the rampart. The archaeologists found remains of defensive fortifications in the rampart, and on the plateau, where the cultural layer thickness ranges from 0.6 to 0.8 meters, they discovered hand-formed pottery with striped, rough, and smooth surfaces, as well as fired ceramics and arrowheads. The settlement area, covering 50 square meters, had a cultural layer thickness of 0.3-0.5 meters. Artifacts found here include hand-formed and fired pottery, remains of iron ore smelting furnaces, and fragments of clay crucibles. Historians believe that the hillfort was used from the early 1st millennium until the 10th-11th centuries, while the settlement was inhabited from the 3rd to the 11th century.