The 1866 Constitution of Romania was the fundamental law that capped a period of nation-building in the Danubian Principalities, which had united in 1859. Drafted in a short time and closely modeled on the 1831 Constitution of Belgium, then considered Europe's most liberal, it was substantially modified by Prince (later King) Carol and adopted by the Constituent Assembly. The newly installed Prince then promulgated it on 13 July [O.S. 1 July] 1866. This was done without input from the major powers, including the Ottoman Empire, which still had formal sovereignty over Romania.