The Province assembly (Parliament) of Eastern Rumelia was designed by architect Pietro Montani and is now one of his most significant creative accomplishments. The building was under construction from 1883 to 1885 under the guidance of architect Oscar Lefait. On 6th of September 1885 the Unification of Eastern Rumelia and the Principality of Bulgaria was proclaimed and the building was deprived of its initial designation. In March 1886 the Prime Minister Petko Karavelov ordered the building to accommodate the public library and museum. Today it is a cultural monument of national importance and home of exposition "The Unification of Bulgaria of 1885".