In the 1930s, Fascism and especially Nazism threatened to change the borders established after the Great War. Countries therefore prepared for conflict by building defence lines along their borders with hostile neighbours. The Kingdom of Yugoslavia also began building a defence line, first on its western border with Italy, and after the annexation of Austria by Germany in 1938, also in Carinthia and Styria. The paper describes the planning, construction, and wartime operation of the defence line, as well as its integration into the landscape. Apart from examining archival sources and reviewing the existing literature, research also included locating individual fortifications in the field, determining their coordinates, and estimating the remaining portions of Sector 6 in Carinthia and Styria.Fašizem in še posebej nacizem sta v 30. letih 20. stoletja grozila, da bosta spremenila meje, določene po »Veliki« vojni. Države so se na obračun pripravljale z gradnjo obrambnih linij na mejah s sovražnimi sosedi. Tudi Kraljevina Jugoslavija je začela graditi obrambno linijo, najprej na zahodu, na meji z Italijo, po priključitvi Avstrije Nemčiji leta 1938 pa še na Koroškem in Štajerskem. V prispevku bo predstavljeno načrtovanje, priprava na izgradnjo in izgradnja linije ter njeno umeščanje v pokrajino in delovanje v aprilski vojni. Poleg preučitve virov in literature je bilo treba poiskati posamezne fortifikacije v naravi, jim določiti koordinate in ugotoviti, koliko delov obrambne linije Kraljevine Jugoslavije, 6. sektorja na Koroškem in Štajerskem, je še ostalo
