The oldest Catholic cathedral is the five-nave Archbasilica of St. John in Lateran erected in Rome, but the Lateran Palace (Latin: Palatium Apostolicum Lateranense) was given as a present to Bishop (Latin: episcopus) of Rome for his residence (from 4th until 14th cent.). The perimeter building set up the structural complex of L-shaped layout where the Lateran Castle and the Archbasilica were included. In Western Europe largest cities were also archbishoprics’ centers, in which neighborhood Catholic church-states, or bishoprics were founded. Local conditions and relationships between the ruler and inhabitants determined the development of Christianity centers. Its main structural objects included in the fortified building complex were the Catholic cathedral which altarpiece (Latin: presbyterium) by the main altar was turned toward the east facing the rising sun, headquarters of the Canonical Chapter (German: Domkapitel) and Bishop's strong fortified residence resembled a lower tower, or a palace separated from the town, or built outside the town. In the late 12th century, bishoprics began to establish on the Baltic Sea southern coast at subjugated lands of the Balts and the Baltic Finns. At bishoprics’ centers Bishops’ fortified yards (German: der Bischofshof) were formed. A housing combined with a sacral structure was included in the perimeter building around the spacious court and integrated into the unified defensive system of the structural complex. In Riga, the Germans established centers of secular and spiritual power, as well as the main military economic base for the Baltics’ expansion. The political and economic dualism was created. The representation of civil authority became the third alternative force. Each of centers characterized by its own structural elements. The main cult building for city inhabitants was the church of citizan’s parish. Research problem: the development of the Catholic cathedral building-type in bishoprics’ towns on the southern bank of the Baltic Sea during the 13th – 14th centuries has been studied insufficiently. Research topicality: the impact of cathedral building complexes on formation of medieval urban structures on the Baltic Sea south coastal lands during the 13th – 14th centuries. Research goal: analysis of the structure and layout of Catholic cathedrals in Livonia and the Prussians’ lands to determine commom and diverse features. Research novelty: evolution of the layout and structure of Catholic cathedrals on lands inhabited by the Baltic etnic groups have been analysed in regional and European context. Results: study formation of the Catholic cathedrals’ layout and structure on the Baltic Sea south coastal lands during the 13th – 14th centuries. Main methods: inspection of cathedrals in nature, analysis of archive documents, projects, cartographic materials.