The article presents preliminary data on the excavations of the Rubas fortification complex in 2020. The archaeological site is located in the lower reaches of the river. Rubas, near the village. Commune of the Derbent region of the Republic of Dagestan, 20 km south-west of the city of Derbent.
 The monument was discovered in 2014 by local residents. The work on its research is carried out by the Rubass archaeological expedition of the Institute of Archeology and Ethnography of the DPhIC RAS (head of the expedition LB Gmyrya).
 In 2014, 2016–2018 four military engineering structures were identified and investigated: 1) an arched tower structure; 2) stone wall No. 1, attached to the arched structure from the north; 3) monumental stone defensive wall No. 2, oriented in the south-north direction (28 m section was explored); 4) stone wall no. 3, attached to wall no. 2 from the east, oriented west-east (section 5 was investigated).
 The excavations were carried out with the financial support of projects by the RFBR-Dagestan (2014) and RFBR (2016–2018) funds. It was established: 1) the undoubted belonging of the archaeological site on the Rubas River to the monumental defensive structures; 2) a complex, multifaceted structure and layout; 3) a variety of technological methods for laying massive blocks into walls; 4) careful processing of stone blocks; 5) the use of a fastening solution using lime and special brackets for fastening the blocks of the facade part of buildings.
 However, the scale of the Rubas defense complex and the uniqueness of its location at the bottom of the Rubas River valley determine the presence of problematic issues related to the topography and planning of this object.