The Kajkavian speech area borders in the northwest on the Slovene language and in the northeast on the Hungarian language. In the east and southeast it is bordered by Shtokavian dialects roughly along a line that used to serve as the border between Civil Croatia and the Habsburg Military Frontier. Finally, in the southwest it borders Chakavian along the Kupa and Dobra rivers. It is thought that historically these borders extended further to the south and east. For example, the eastern border is thought to have extended at least well into modern-day Slavonia to the area around the town of Pakrac. Some historical toponyms suggest a slightly larger extent.