Use of whistles to relay commands in battle

[Thomas Aagaard]

An 1899 drill manual says that they're only used for calling attention to the officer before he gives an order

Iam not doing roman reenactment. But I do have some exerience with late medieval periode fighting with a polearm/pike unit. We use wood whistles before the "officer" gives his order just like descriped in the quote. It really helps the men in the line focus on the order. Without the whistle the order is much more likely to be drowned out by the sound from the combat.

I have no idea if the romans used it, but it works with a 30man unit so I do believe it would have help the centurions too.