The eleventh and twelfth centuries witness the growth of a strong government in central Europe. The Holy Roman Empire, as the union of Germany and the northern Italian principalities under a German emperor came to be known, temporarily asserts its authority even over the Church, and both are energetic patrons of the arts. By the thirteenth century, imperial power begins to decline, while the autonomy of principalities, prince-bishoprics, and cities increases. The emperor and the pope, as the leading patrons of the arts in the High Middle Ages, are emulated by lesser rulers and city governments.