In O Magnum Mysterium, Tomas Luis De Victoria uses basic rhythms (whole notes, half notes, quarter notes, eighth notes) in various ways to make the music interesting.  There is nothing particularly exceptional about the way he uses these rhythms.  One thing that does capture my attention in this piece is how he layers the rhythms on top of one another.  He tends to switch back and forth between homo-rhythmic passages and poly-rhythmic passages.  He begins the piece with a single voice, and begins the next voice six beats later creating a round or fugal feel.  Then the rhythm becomes homo-rhythmic in the top two voices in measure 9 with the fugue continuing in the third and fourth voices.  All four voices share the same rhythm from measure 20 to measure 25.  The voices all have different rhythms across the score until the fourth beat of measure 39, which then turns back into homo-rhythmic for the next four measures.  When we get to measure 52, there is a meter shift from 4/4 to 3/2.  It stays mostly homo-rhythmic.  At measure 58 there are at least two voices continually moving together until the meter shift back to 4/4 when the voices finish the piece in poly-rhythm.  The one thing that stands out to me the most while listening to this piece is that there is always at least one voice singing a quarter note on each beat.  This gives the piece consistent pulse which provides the feeling of forward motion in the music.  For the period of time in which it was written, I think that this was a fairly standard method of notation which may have helped performers stay in time together without a conductor or a percussionist giving the tempo to the ensemble.  I feel that the meter shifts were the only exceptional or possibly “new” technique used in writing this piece.