During 2nd century BCE to 6th century CE in Deccan Plateau of Western Ghat a huge number of rock-cut caves were carving by the Buddhist monks mainly to stay during the monsoon time because due to continuous raining it was not possible to go in the surrounding villages for begging.
The monsoon continues approximately for two and half years in Sahaydri range of Western Ghat, so they need a shelter to stay for this period. The huts made up of clay, bamboo and straw materials are not enough strong to withstand the water flows, hilly winds and constant rains. So, they decided to carve the solid basalt rocks into caves where they can stay permanently. Position wise they tried to find out that kind of hills those are getting direct morning lights from the Sun and opposite to the Arabian Sea, so the Indian monsoon current will flow from the back side of the hills.
In searching of these kind of hills they carved the rock-cut caves in a scattered area of Maharastra and these places were connected to the trade route from Arab to South India using Arabian Sea. The traders using these route and started to spend the night time for resting purpose in these caves. As a result they donate something for the caves to monks. Interestingly mostly all the caves were carved besides the villages, where a river was in surrounding place and well skilled water system managements (still now you can see) are present using the rain water during the monsoon.
There are mainly two forms of Buddhist caves, one is Vihara-form and other one is the Chaitya-form. The word Chaitya means the prayer hall whereas Vihara refers to the monastery for the Buddhist monks. In Pali or early Sanskrit the Vihara refers to an architectural concept where the living quarters present with an open shared space or courtyard. It was kind of arrangement of space or facilities for pleasure and entertainment for the monks or nuns referring to temporary refuge for wandering during the annual Indian monsoons.
There is a chronology of the Chaitya cave formation in Western India during the period of 1st century BCE to 6th century CE and all the caves which had been built under royal sponsorship.
Gradually the skill and ornamentation of the Chaitya forms were developed. If you notice mindfully the earlier caves are not that much ornamented. The pillars are in simple octagonal form with simple base and capitals. But, if you notice the pillars of later Chaitya caves where the rock-cut carves of the base and capital are well decorated and ornamented with animals, male, female and different kind of signs.
The two Chaitya caves of Ajanta and one from Pitalkhora are for Mahayana Buddhist tradition where a Buddha idol present inside the cave, whereas the other seven Chaitya forms are of Hinayana tradition where only a stupa is present the caves.
It is thought that around the 1st century BCE the chronology of these early Chaitya Caves are as follows:
|First: Chaitya Cave @Kondivite, Andheri, Mumbai|
|Second: Chaitya Cave @Bhaja, Lonavla, Pune|
|Third: Chaitya Cave @Ajanta cave no. 10, Aurangabad|
|Fourth: Chaitya Cave @Pitalkhora, Aurangabad|
|Fifth: Chaitya Cave @Kondana, Karjat, MH|
|Sixth: Chaitya Cave @Ajanta, cave no 9, Aurangabad|
|Seventh: Chaitya Cave @Budhha leni, Nasik|
|Eighth: Chaitya Cave @Bedse, Kamshet, Pune|
|Ninth: The Great Chaitya, final perfection and penultimate product @Karla, Lonavla, Pune (120 BCE)|
I have written some of the Chaitya form caves separately in 'My Interest' tab of my blog. You can get the details for each cave from that segment.