Volley Fire in Ancient Armies

[Eleatic Guest]

What evidence do we have for the theory and practice of volley fire in antiquity and what passage in Aelian might have inspired Maurice?

In 1594, William-Louis of Nassau had written to his cousin Maurice, suggesting salvo fire, or volley fire by ranks, a tactic that he had discovered in his reading of Aelian. Following the practice of the ancients, he proposed that each rank of shot would discharge its weapons at once, and then smartly retire to the rear while reloading. By this method he assumed that a continuous rolling fire could be kept up.

Philosophers of War: The Evolution of History's Greatest Military Thinkers , p. 120

Just noticed the same question already came up on this forum...ten years ago!