This is the first period where we can begin to be fairly certain as to how a great deal of the music which has survived actually sounded. The earliest written secular music dates from the 12th century troubadours (in the form of virelais, estampies, ballades, etc.), but most notated manuscripts emanate from places of learning usually connected with the church, and therefore inevitably have a religious basis. Gregorian chant and plainsong which are monodic (i.e. written as one musical line) gradually developed during the 11th to 13th centuries into organum (i.e. two or three lines moving simultaneously but independently, therefore almost inadvertently representing the beginnings of harmony). Organum was, however, initially rather stifled by rigid rules governing melody and rhythm, which led ultimately to the so-called Ars Nova period of the 14th century, principally represented by the composers de Vitry, Machaut, and Landini.