The pipe organ, built from ranks of wood, tin and lead pipes fed by a wind supply and controlled through keyboards, did not begin as a church instrument at all; its ancestor, the hydraulis, was a Greek and Roman invention used for public entertainment and imperial ceremony centuries before any Christian church adopted it.
The Cambridge Companion to the Organ traces the instrument's gradual movement into Western Christian worship across the early medieval period, a process that unfolded over centuries rather than through any single dramatic introduction, until the organ became established by the high medieval period as the characteristic instrument of Western church music, a status essentially unmatched by any other instrument across the following thousand years of Catholic and, later, much Protestant liturgical practice. Its physical scale grew accordingly, and the largest cathedral and concert organs represent genuine feats of acoustic and mechanical engineering, some containing many thousands of individual pipes tuned and voiced to work together as a single unified instrument. The organ's keyboard mechanism itself, developed and refined across the medieval and early modern periods, became a technical foundation later keyboard instruments, including the harpsichord and eventually the piano, drew on directly, so the organ's influence on Western music extends well beyond church repertoire alone.