The polyphony of Christian a cappella music began to develop in Europe around the late 15th century, with compositions by Josquin des Prez. The early a cappella polyphonies may have had an accompanying instrument, although this instrument would merely double the singers' parts and was not independent. By the 16th century, a cappella polyphony had further developed, but gradually, the cantata began to take the place of a cappella forms. 16th century a cappella polyphony, nonetheless, continued to influence church composers throughout this period and to the present day. Recent evidence has shown that some of the early pieces by Palestrina, such as what was written for the Sistine Chapel was intended to be accompanied by an organ "doubling" some or all of the voices. Such is seen in the life of Palestrina becoming a major influence on Bach, most notably in the aforementioned Mass in B Minor. Other composers that utilized the a cappella style, if only for the occasional piece, were Claudio Monteverdi and his masterpiece, Lagrime d'amante al sepolcro dell'amata (A lover's tears at his beloved's grave), which was composed in 1610, and Andrea Gabrieli when upon his death it was discovered many choral pieces, one of which was in the unaccompanied style. Learning from the preceding two composeres, Heinrich Schütz utilized the a cappella style in numerous pieces, chief among these were the pieces in the oratorio style, which were traditionally performed during the Easter week and dealt with the religious subject matter of that week, such as Christ's suffering and the Passion. Five of Schutz's Historien were Easter pieces, and of these the latter three, which dealt with the passion from three different viewpoints, those of Matthew, Luke and John, were all done a cappella style. This was a near requirement for this type of piece, and the parts of the crowd were sung while the solo parts which were the quoted parts from either Christ or the authors were performed in a plainchant.
Who's compositions marked the begining of secular a cappella music (If the question is unanswerable, say "unanswerable")
unanswerable