At Nāḷandā 6.5

6.5

So tassa nagarassa samantā anupariyāyapathaṃ anukkamamāno na passeyya pākārasandhiṃ vā pākāravivaraṃ vā, antamaso biḷāranikkhamanamattampi.

As he walks around the patrol path, he doesn’t see a hole or cleft in the wall, not even one big enough for a cat to slip out.