These instruments are found in parts of the Empire where they did not originate and indicate that music was among the aspects of Roman culture that spread throughout the provinces. Instruments are widely depicted in Roman art. The hydraulic pipe organ (hydraulis) was "one of the most significant technical and musical achievements of antiquity", and accompanied gladiator games and events in the amphitheatre, as well as stage performances. It was among the instruments that the Emperor Nero played. Although certain forms of dance were disapproved of at times as non-Roman or unmanly, dancing was embedded in religious rituals of archaic Rome, such as those of the dancing armed Salian priests and of the Arval Brothers, priesthoods which underwent a revival during the Principate. Ecstatic dancing was a feature of the international mystery religions, particularly the cult of Cybele as practiced by her eunuch priests the Galli and of Isis. In the secular realm, dancing girls from Syria and Cadiz were extremely popular. Like gladiators, entertainers were infames in the eyes of the law, little better than slaves even if they were technically free. "Stars", however, could enjoy considerable wealth and celebrity, and mingled socially and often sexually with the upper classes, including emperors. Performers supported each other by forming guilds, and several memorials for members of the theatre community survive. Theatre and dance were often condemned by Christian polemicists in the later Empire, and Christians who integrated dance traditions and music into their worship practices were regarded by the Church Fathers as shockingly "pagan." St. Augustine is supposed to have said that bringing clowns, actors, and dancers into a house was like inviting in a gang of unclean spirits. Literacy, books, and education Estimates of the average literacy rate in the Empire range from 5 to 30% or higher, depending in part on the definition of "literacy". The Roman obsession with documents and public inscriptions indicates the high value placed on the written word. The Imperial bureaucracy was so dependent on writing that the Babylonian Talmud declared "if all seas were ink, all reeds were pen, all skies parchment, and all men scribes, they would be unable to set down the full scope of the Roman government's concerns." Laws and edicts were posted in writing as well as read out. Illiterate Roman subjects would have someone such as a government scribe (scriba) read or write their official documents for them.