SB 10.12.16
iti vyavasyajagaram brhad vapuh
sa yojanayama-mahadri-pivaram
dhrtvadbhutam vyatta-guhananam tada
pathi vyaseta grasanasaya khalah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
After thus deciding, that crooked Aghasura assumed the form of a huge python, as thick as a big mountain and as long as eight miles. Having assumed this wonderful python’s body, he spread his mouth like a big cave in the mountains and lay down on the road, expecting to swallow Krsna and His associates the cowherd boys.