The Slavic, also known as Pan-Slavic theory, about the idea that the Slavs came to Illyricum from Poland is of old origin at least since the 12th century. With the development of Croatian historiography since the 17th century was elaborated in realistic terms, and considered Croats as one of the Slavic groups which settled in their modern-day homeland during the migration period. Constantine the VII's work was particularly researched by the 17th century historian Ivan Lučić, who concluded that the Croats came from White Croatia on the other side of the Carpathian mountains, in Sarmatia (Poland), with which historians today agree upon.