A small Stupa enclosed within a circular shrine with a domical roof of wooden construction supported on pillars and known as Ambasthala Dagaba is the first monument that we see after entering the upper terrace of Mihintale.
The historical records give reference to three Stupas on the summit of the Mihintale hill. These are Sila Cetiya, Ambastala Cetiya and the Mihindu Saya. The first of these three is believed in medieval times to have been built on the spot where the Buddha himself reputedly spent some time, seated in meditation on his third visit to Sri Lanka.
The Ambastala Cetiya, the second, was built by Mahadatika Mahanaga (9-21 A.D.). The third one was built by Uttiya (210-200 B.C.) to enshrine a portion of Mahinda Mahathera’s ashes.
The Pujavaliya refers to the Sila Cetiya as Mahasalasa and says that it was put up on the spot where the Buddha sat in meditation. According to an inscription on the stone terrace of the Stupa and on a broken down pillar these stone pillars were the work of the seventh century.
A Cetiyaghara or a house enclosing this small Stupa was built at the beginning of the Christian era. According to the Mahavamsa King Kanittha Tissa (167-186 A.D.) is said to have built a Cetiyaghara at Ambasthala. This was repaired by King Gothabhaya (249-262 A.D.).
In both these references, it is the Cetiya or Tupaghara and not the dagaba itself that is mentioned. Therefore, the dagaba must have been in existence before these two Kings. The Habarana inscription mentions a land grant for the maintenance of the Cetiya – house built for the Sila Cetiya at Ambastala by a King, who it can be inferred from the script, ruled the country in the third century.
Further, the Mahavamsa also informs us that King Kutakanna Tissa (44-22 B.C.) built a stone Dagaba at Cetiyapabbata in front of a great uposatha – house which he himself established.
At this spot he is also said to have planted a Bodhi tree. The Bodhi tree is front of the Sila Cetiya can be the same or another that was planted on the spot. The popular belief is that the present Bodhi tree was planted by King Devanampiyatissa himself.
Near the Sila Cetiya and behind the Bana-maduwa or the modern preaching hall is a rock on which the inscription is written in a script similar to the grantha letters but in Sanskrit. It has twenty one lines.
This inscription contains a clear reference to the teachings of the three bodies of the Buddha (trikaya) accepted by the Mahayana Buddhists.