This stupa had been excavated and restored in 1951. Approximately 25 meters in circumference. The stupa was restored up to about 8 meters of height and has been dated to 8th century.

Mihintale

Mihintale is a mountain peak near Anuradhapura in Sri Lanka. It is believed by Sri Lankans to be the site of a meeting between the Buddhist monk Mahinda and King Devanampiyatissa, which inaugurated the presence of Buddhism in Sri Lanka. It is now a pilgrimage site and the site of several religious monuments and abandoned structures.

Approximately 12.5 km (7.8 mi) east of Anuradhapura, close to the Anuradhapura - Trincomalee Road is situated the "Missaka Pabbata" which is 1,000 feet (300 m) in height and is one of the peaks of a mountainous range.

According to Dipavamsa and Mahavamsa, Thera Mahinda came to Sri Lanka from India on the full moon day of Poson (June) and met King Devanampiyatissa and preached the Buddhist doctrine. The Buddhists of Sri Lanka revere the traditional spot where this meeting took place. Therefore, in the month of Poson, Buddhists make their pilgrimage to Anuradhapura and Mihintale.

Mahinda was the son of Emperor Ashoka of India. King Ashoka embraced Buddhism after he was inspired by a monk named "Nigrodha." The King was in great misery after witnessing the devastation caused by expansionist wars. Meeting this peaceful young monk was a turning point in his life; after that, he renounced war. He was determined to spread the message of peace. As a result, both his son and daughter were ordained as Buddhist monastics and became enlightened Arahats. In his quest to spread the message of peace instead of war, Ashoka sent his son Mahinda to Lanka, which was also known as "Sinhalé". This island was ruled by his friend King Devanampiyatissa. Thus, "Mahinda" was the Indian name, which in Sinhalé became "Mihindu."

In Sinhala, Mihin-Thalé means the "plateau of Mihindu". This plateau is on top of a hill from where Arahat Mihindu was supposed to have called King Devanampiyatissa, by the King's name to stop him shooting a deer. Hence, "Mihin Thalé" is a specifically Sinhala term.

From ancient times, giant steps were constructed to climb Mihintale. It is stated that King Devanampiyatissa built a vihara and 68 caves for the bhikkhus to reside. At Mihintale, there gradually grew several Buddhist monasteries or viharas with all the dependent buildings characteristic of the monasteries of that period.

Wikipedia

The sites

https://www.lanka-excursions-holidays.com/mihintale-attractions.html