Use of whistles to relay commands in battle

[Titus Marius Secundus]

Surely whistles must have been used in battle during some period of the legions. In the TV series Rome, they show this and how effective it is for changing ranks. Now tell me, what better way could you signify a change in ranks every 5 minutes other than a whistle blow. A blow of a horn maybe. It could vary no? If there's only one finding of a whistle on any military grounds or battle fields, then I would say its unlikely they were used much at all. Maybe by older time periods before the Imperial stage? And also, whistles are known to be made of wood, thus decreasing their chances of survival... ( they are small objects, and by the amount of land we actually do excavate, I doubt we'll find one if it's there, thus no recorded usage of them)

Hope this enlightens a little,

Sam