“The rowers did not sit, but Stood in an inclining position. The practice was directed by a person called celeustes the Roman hortator remigum who was placed in the middle of them, and carried a staff, with which he gave the signal when his voice could not be heard. This signal was for the rowers to strike; and he encouraged them by a song or cry, called the celeusma. This was either sung by the rowers, or played upon instruments, or effected by a symphony of many or striking sonorous tones.”
[A Treatis on the Arts, Manf, Manners, Inst of the Greeks & Romans, Vol.I, Fosbroke, 1833, pp.211-212]