Gregorian chant was the dominant form of music in medieval Europe, sung without instrumentation in monasteries and cathedrals to accompany mass. In the 12th century, composers like Leonin and Perotin began adding voices to chant to create early polyphonic music known as organum. Major composers like Machaut expanded church music through works like his Messe de Nostre Dame. Secular music also developed through the Troubadours and Trouveres who composed songs of courtly love. Instrumental music was limited but included precursors to modern instruments as well as pipe organs.