People occupy more spaces than you might think.
Even if you put people beside each other, shoulder to shoulder, each person will occupy at least 50 cm. That is without any armour or equipment on them. If they are wearing chain mails and other defensive equipment, they will need at least half a meter to a meter or even two meters to move freely. If you put 300 men in a line, you will need at least 300 meters to align them( if you consider each person needs a meter of space). You won't find such space in a mountain or a forest region that often.
