The high medieval works of fourteenth-century composer Guillaume de Machaut, with their characteristic texture of a quick top voice, slower middle voice, and a long-note "tenor," are great pieces, and like all great pieces they make the basic style in which they are written seem somehow inevitable. Yet that style was not inevitable. Someone had to work out the texture of fast, medium, and slow -- of chipper, talkative top voice underlaid with a dour middle line, and a few long notes of chant for the bottom. That someone was Petrus de Cruce.
His immediate predecessor was Franco of Cologne, a composer active in the years after 1250. Franco developed the form of the polytextual motet -- generally a three-part vocal composition with a different text for each part. The various texts might complement or contradict each other; one might be secular and another sacred; they might even be in different languages (French or Latin).
The listener who is flummoxed by this configuration is on the right track, for the polytextual motet was a complex form, not a simple one. Petrus, who worked at the end of the thirteenth century, made it more complex yet. His main innovation was to increase the number of possible subdivisions of the "breve" -- the shorter of the two main rhythmic units of medieval music. In the music of his predecessors, each breve might be divided into a "perfect" three semibreves or into an "imperfect" two. Petrus, widely recognized as both theorist and composer, posited instead that the breve might be divided into as many parts as the composer wished. (In practice he used up to seven.) The result was the so-called Petronian motet, with a top line that trips along at a speed that the age of opera would call [parlando. His pieces, of which perhaps eight survive, are mysterious for modern listeners, but the modern concept of melody both subtly linked to the demands of text and artfully accompanied by music in longer note values is there in chrysalis stage.
As with most other medieval composers, little is known of Petrus' life. In fact he is one of the few thirteenth-century composers who has been identified by name. Sometimes known by the French form of his name, Pierre de la Croix, he was a Parisian churchman, the scion of a powerful family in Amiens.