A complex of three Roman castles. http://bulgariancastles.com/bg/node/1363 https://www.academia.edu/5737000/V._Dintchev._The_East-Balkan_Barrier_Wall_and_the_Gates_of_Haemus_Complex._-_In_The_Lower_Danube_Roman_Lines_1st-_6th_C._AD_._Sofia_2012_495-526