The period A.D. 600-1400 is here referred to as the medieval period. During these Middle Ages liturgical chant and secular solo public singing saw their greatest development. Polyphony reached fine artistic forms and Gregorian chant had its beginning then, as did Ambrosian chant in the north, the Gallican in France, and Visigothic in Spain. A need for a unified liturgy became most apparent as each geographical section argued its own pre-eminence over Rome until the eleventh century, when the Roman liturgy was universally enforced, with a few limited exceptions. The years between 700 and 800 saw all chants embellished with new words, preludes, and interludes. Sequences had their beginning in the twelfth century and became so elaborate that the Council of Trent felt forced to ban all of them except Lauda Sion, Veni Creator Spiritus, Victimae Paschali Laudes, and Dies Irae, admitting Stabat Mater a little later. A large repertory of secular melodies made their appearance in the same century, but after Rome's fall their impact, musically, was slight. Troubadour melodies appeared in the South of France, spread to the north, then to the German minnesingers. The troubadours occupied prime positions in medieval musical history, with Spain, Italy, and England producing much devotional song composition. The thirteenth century saw the motet developed, using sacred texts, but later the liturgical aspects of the words were lost, dance tunes and troubadour melodies taking their place. Different rhythms were of great interest in the mid-thirteenth century; three-part rhythm dominating in polyphonic music. The ballad form appeared in the fourteenth century, with ornate rhythmic patterns evolving and unusual syncopations being tried. As the period closed a new musical impetus came from England -- the new art exploiting thirds and sixths, very important to music.