Who were the builders of Karlovac?

The Osmanli military campaign in Europe prompted the construction of a defence system in which many nations and countries of the Habsburg Monarchy participated, including also a large part of the Croatian Kingdom. The Pokuplje region and the area to its south, known as Hrvatska Vojna krajina, were governed by the War Council of Graz, after whose chief commander, the Grand Duke Karlo Habsburg, the city of Karlovac was named.