In 395, the Roman Empire was divided in the Western Roman Empire (Latin: Imperium Romanum Occidentale) and the Eastern Roman Empire (Latin: Imperium Romanum Orientale, Romania), or Byzantium. On capital city Constantinople (today Istambul in Turkey) western side, a strong defensive wall was built, creating triple planning. In Russia, where in the 10th century Christianity was adopted, building traditions of the Orthodox believers’ lands affected, but in the second half of 11th century, it was introduced in Latgalia. In German lands, two-part planning was made to Wartburg Fortress (1067–1075) after its reconstruction (1140–1172), separating the castle- front from the ruler’s residence. In Livonia, architectural structures of fortified buildings, created by Germans, was supplemented with a castle settlement, which in triple planning developed as a separate structural unit. Current researches: American geographer John Leighly (1895–1986) on the basis of local features grouped fortified complexes of Fellin (Estonian: Viljandi), Wolmar (Latvian: Valmiera) and Kokenhusen, emphasising link of Livonian castles with the town. Estonian historian of architecture Elmo Raadik (1925–1969) together with prof. Dr. art. Voldemar Vaga (1899–1999) worked out a research “Viljandi arhitektuuri ajalugu feodalismi perioodil (XIII–XIX sajandi keskpaigani)” (1960). Latvian historian, archivist Roberts Malvess (1905–1982) compiled “Building History of Kokenhusen Castle. The 13th century–20s of the 17th century” (2010), but Dr. hist. Tatjana Berga conducted archaeological research of Wolmar Castle (1988–1996) (2002). Historical, archaeological, architectonic research materials of Livonian fortresses have been included into series “Latvian Medieval Castles” published by Latvia History Institute. Estonian archaeologists Aare Kodar and Dr. Erki Russow published a new research “On Development of Town of Viljandi in Light of Earliest Archaeological Find Complexes” (2013). The impact of Byzantium fortified urban building structure traditions on the 13th century German administrative centres planning in Livonia has been studied insufficiently.