Kautilya's Arthashastra 2.3.14

2.3.14

daṇḍāntarā dvidaṇḍāntarā vā caryāḥ kārayet, agrāhye deśe pradhāvanikāṃ niṣkiradvāraṃ ca //

Paths (chárya, to ascend the parapet?) as broad as a danda (6 ft.) or two shall also be made.

In an unassailable part (of the rampart), a passage for flight (pradhávitikám), and a door for exit (nishkuradwáram) shall be made.