The Hillfort, dating back to the middle of the 1st millennium – early 2nd millennium, surrounded by valleys of rivulets on the northern, western and southern sides, is called differently as well: Zamkus or Zamkelis. The hillsides are steep, 8–11 m high. The site is oval in shape, about 45 m long and 21 m wide. A rampart 170 m long (1–4.5 m high) surrounds the Hillfort in a circle. There are four pits on the site, which remained as amateurish excavations by German troops in 1916–1917. North and east of the Hillfort foot, across the rivulet, an ancient settlement was discovered. A cultural layer of up to 0.5 m thickness was found with the fragments of handmade plain and coarse surface pottery and a brooch, loop type, containing a triangle stem.
Geruliai Hillfort is included into the Register of Immovable Cultural Properties.