Johann Matthias Gesner was a colleague of Johann Sebastian Bach at St. Thomas’ School, Leipzig. He later worked on a commentary of the Roman author Quintilian (c. 35-100 A. D.). He included a comparison of Bach with the Classical lyre player:

All these (outstanding achievements) … you would reckon trivial could you rise from the dead and see our Bach … how, with both hands and using all his fingers, he plays a clavier which apparently consists of many citharas in one, or runs over the keys of the king of instruments, whose innumerable pipes are made to sound by means of bellows; and how, going in one direction with his hands, and in another direction, at the utmost speed, with his feet, he conjures up unaided … hosts of harmonious sounds; I say, could you but see him, how he achieves what a number of your cithara players and 600 performers on wind instruments could never achieve, not merely . singing and playing at the same time his own parts, but presiding over thirty or forty musicians at once, controlling this one with a nod, another with a stamp of his foot, a third with a warning fingers, keeping time and tune, giving a high note to one, a low to another, and notes in between to the rest. This one man, standing by himself in the middle of the loud sounds, having the hardest task of all, can tell at any moment if anyone goes astray, and can keep all the musicians in order, restore any waverer to certainty and stop him from going wrong. Rhythm is in his every limb, he takes in all the harmonies by his subtle ear and voices all the different parts through his own mouth … I reckon this Bach of mine to comprise in himself many Orpheuses and twenty Arions (1).

Source: Dowley, Tim (1981) Bach. London: Omnibus Press, p.94-95.

(1) Orpheus was an ancient Greek poet and musician. He was labelled by Pinda as “the father of songs”). He would gain legendary status in ancient Greek mythology for his ability to charm living things with his poetry and music, and his attempt save his wife, Euridice, from the underworld. Mythological elements of Orpheus would be revived in operas by Monteverdi (L’Orfeo) and Gluck (Orfeo ed Euridice), amongst countless other interpretations in other genres of the arts.
Arion was an ancient Greek poet credited with inventing the dithyramb – a hymn and dance of praise in honour of the God of wine and fertility, Dionysus.

(2) Pinda, Pythian Odes, 4.4.315