The boundaries of Croatia proper were shaped by territorial losses of medieval Croatia to the Republic of Venice and the Ottoman conquest starting in the 15th century. In effect, Croatia proper loosely corresponds to what was termed "reliquiae reliquiarum olim magni et inclyti regni Croatiae" (the relics of the relics of the formerly great and glorious Kingdom of Croatia) and the subsequent Kingdom of Croatia within the Habsburg Monarchy. The region contains most of the 180 preserved or restored castles and manor houses in Croatia, as it was spared any large-scale war damage throughout its history. Varaždin and Zagreb occupy prominent spots in terms of culture among the region's cities. The west of the region represents a natural barrier between the Adriatic Sea and the Pannonian Basin, and this, along with Ottoman conquest and resulting military frontier status, has contributed to the relatively poor development of the economy and infrastructure of that area.