As to the Tibiæ Serranæ, some have supposed that they were so called from Serra, since they produced the sharp grating sound occasioned by a saw(605); some, that they were denominated Sarranæ from Sarra, a city in Phœnicia, where such flutes are believed to have been invented(606); and others, that they derived their name from Sero to lock; because in these flutes, there were valves or stops which opened and shut alternately(607). It is only farther known, that the Tibiæ Serranæ belonged to the class called Pares, and the Phrygiæ, to which they were opposed, to that styled Impares. All flutes, of whatever denomination, were extremely simple in the commencement of the dramatic art at Rome. Their form was plain, and they had but few notes. In progress of time, however, they became more complex, and louder in their tones(608). Several chorded instruments were also used in the orchestra, as the lyre and harp, and in later times an hydraulic organ was introduced. This instrument, which is described in the _Organon_ of Pub. Optatianus, emitted a sound which was produced from air created by the concussion of water. Cornelius Severus, in his poem of _Ætna_, alludes to it, under the name of _Cortina_— “Carmineque irriguo magni Cortina Theatri Imparibus numerosa modis canit arte regentis, Quæ tenuem impellens animam subremigat undam(609).” 3. _The Stage_. The front area of the stage was a little elevated above that part of the orchestra where the musicians were placed, and was called the _Proscenium_. On the proscenium a wooden platform, termed the _pulpitum_, was raised to the height of five feet(610). This the actors ascended to perform their characters; and here all the dramatic representations of the Romans were exhibited(611), except the Mimes, which were acted on the lower floor of the proscenium. Certain architectural proportions were assigned to all these different parts of the theatre.