The pneumatic organ is sculptured on an obelisk which was erected in Constantinople under Theodosius the great, towards the end of the fourth century. The bellows were pressed by men standing on them: see page 103. This interesting monument also exhibits performers on the double flute. The hydraulic organ, which is recorded to have been already known about two hundred years before the Christian era, was according to some statements occasionally employed in churches during the earlier centuries of the middle ages. Probably it was more frequently heard in secular entertainments for which it was more suitable; and at the beginning of the fourteenth century appears to have been entirely supplanted by the pneumatic organ. The earliest organs had only about a dozen pipes.