One of the five mountains round Rājagaha and one of the beauty-spots of the city (D.ii.116). There was, on one side of it, a black stone called the Kālasilā. This was a favourite haunt of the Buddha and the members of the Order. See e.g., Viii.ii.76, where Dabba Mallaputta is asked by monks to provide for them accommodation there; see also Vin.iii.41.
It was also the scene of the suicide of Godhika and Vakkali (S.i.121; iii.121f) and of the murder of Moggallāna by the brigands (J.v.125f; DhA.iii.65).
In the Cūla Dukkhakkhanda Sutta it is said that a large number of Niganthas lived at Kālasilā, never sitting down, undergoing paroxysms of acute pain and agony, following the teachings of Nigantha Nātaputta. The Buddha questioned them as to their practises and preached to them the above-mentioned Sutta, which he afterwards repeated to Mahānāma (M.i.91ff).
Once when the Buddha was dwelling at Kālasilā, he sang the praises of Rājagaha, giving Ananda a chance, if he so desired, of asking him to live on for a kappa; but Ananda did not take his opportunity (D.iii.116).
The books refer to several other visits of the Buddha to Isigilapassa. During one of these visits he heard Vangīsa's high eulogy of Moggallāna (S.i.194; Thag.1249ff).
In the Isigili Sutta (M.iii.68-71) the Buddha is represented as saying that while the other mountains round Rājagaha - Vebhāra, Pandava, Vepulla and Gijjhakūta - had changed their old names, Isigili retained its former name and designation.
Five hundred Pacceka Buddhas once resided in Isigili for a long time; they could be seen entering the mountain, but once entered, there was no more sign of them. Men, observing this, said that the mountain swallowed up the sages and so it came by its name of Isigili (Isī gilatī ti = Isigili).
Buddhaghosa adds (MA.ii.889) that when the Pacceka Buddhas returned from their begging rounds, the rock would open like a folding door to admit them. Within the rock they had made for themselves cloisters, dwelling-houses, etc.