पत्तयोऽश्वा रथा हस्तिनश्चानुपृष्ठमचलः ॥ कZ_१०.६.४० ॥
pattayo 'śvā rathā hastinaś cānupṛṣṭham acalaḥ
In the ‘Acala’ array, infantry, cavalry, chariots, and elephants are arranged successively, one behind another (in depth).
It simplifies command by clear sequencing of echelons and enables staged reinforcement—units can be committed in order as conditions evolve.