Kragujevac was the first capital of modern Serbia ( 1818 -- 1839 ) , and the first constitution in the Balkans was proclaimed in this city in 1835 .
Historically , Kragujevac was the first capital of free Serbia ( from 1818 to 1839 ) , and the first constitution ever proclaimed in Balkans was in this city on February 15 , 1835 ( state holiday ) .