When I read something like Caesar's commentaries, or really any historical account of warfare, troops are 'raised' at certain junctures. Little detail is given about this, but it seems like an enormous oversight. If, for example, the legions of Rome in 50 BC were tough, well-trained, well-equipped men that met certain other criteria, how could Caesar or Pompey or anyone raise a legion quickly?
Again, leaning on Caesar as my example, he raises legions at a few points as he's returning to Italy and preparing to make his push. How would they get that much chain mail? Thousands of shields and pila? The food and other equipment, like mules and tents? When the state has time to prepare and deliver, its easy to see how an armed host comes into being. But as a commander in the field, even with nearby cities or towns under your control, how do you simply manifest a new body of troops?
Is it expected that the quality of such a force would be diminished? Do you just expect higher casualties for a green unit like this? Or am I misunderstanding how long it actually took to train a man? Would towns have had stores of legionary gear?