500 Years in a Nutshell!

For those who find the five hundred or so years of music prior to Monteverdi (c.1600) hard to get a handle on (as I did for many years), I thought that a little chronological guide, complete with YouTube links, to a few of the landmark composers across those many centuries might be a helpful starting point and might reveal, in the simplest and most direct way, just how music changed over that period. Even if it doesn't help much, there's some exceptionally beautiful music to be found at the end of every click!

Hildegard of Bingen, 1098-1179, O frondens virga (single-part chant, sometimes with drone)
Leonin, 1150s-?1201, Dulce lignum (two-part polyphony)
Perotin, c.1200, Viderunt omnes (three- and four-part polyphony)
Adam de la Halle, ?1237-1288, Bonne amourete me tient gai - Dame, or sui traïs (polyphonic secular song)
Guillaume de Machaut, c.1300-1377, Messe de Notre Dame (ars nova, isorhythmics, growing complexity)
Solage, late 14th Century, Fumeux fume par fumee  (ars subtilior, even great complexity)
John Dunstable, c.1390-1453, Veni Sancte Spiritus ('the English countenance', a new simplicity, the advent of Renaissance music)
Guillaume Dufay, c.1397-1474, Balsamus et munda cera (the Burgundian School, fauxbourdon, the birth of Renaissance music).

Johannes Ockeghem, d.1497, Missa Prolationum (the Franco-Flemish School, beginnings of distinctive Renaissance polyphony, growing emphasis on homogeneity of texture)
Josquin des Prez, c.1450-1521, In principio erat verbum (greatest composer of the Franco-Flemish School, the rise of an international polyphonic style)
Giovanni Pierluigi da Palestrina, ?1526-1594, Sicut Cervus, (Roman School, culmination of Renaissance polyphony) 
Orlande de Lassus, ?1532-1594, Timor et tremor (mature polyphonic style of the Franco-Flemish School, intimations of 'modern' style)
William Byrd, ?1540-1623, Haec dies (the international Renaissance polyphonic style in England, the greatest English composer of the Renaissance)
Tomas Luis de Victoria, 1548-1611, O magnum mysterium (the international Renaissance polyphonic style in Spain, the greatest Spanish composer of the Renaissance, and probably of all time)
Giovanni Gabrieli, c.1555-1612, Hodie completi sunt (from the Renaissance to the Baroque)

Claudio Monteverdi, c.1567-1643 Deus in Adjutorium (the Baroque!)