Ring wells have been excavated before in Enkandiyur (Thrissur) (1950s), Edapally (1989) and in Vellayani with a depth of up to 14 rings in 1995. However, most of them have been recovered in a `disturbed' state as was also the case today owing to their proximity to habitation.

Excavation assistant P Sreedharan of the Directorate of Archaeology said the ring wells which were of fine baked clay could have been used for the ``soakage of refuse water''.

The suspected archaeological matter was spotted below a pipeline at Puthan Road, Attakulangara, on Saturday by some contract workers engaged in repair works. The local people who suspected a `treasure trove' reported the matter to the police and archaeologists who rushed in.

Thearchaeologists who at first suspected an urn burial today excavated three rings of the well by the quadrant method after hours of operation.

According to Padmanabhan Thampy, project director marine archaeology, and Sreedharan of the Directorate of Archaeology here, the rings were of 20 cm height and 50 cm diameter.

However, water collected in the surrounding area prevented any further excavation. The antiquity of the well has been determined by the comparative method since there was no scope for carbon dating, he said.

Ring wells have been excavated intact from different parts of the country including Purana Khila, Ahar, Kamparmeda, Mathura, Ujjain, Nevasa and Somnath.

Thampy said ``Thiruvananthapuram which is built on 11 hills'' has a cultural continuity and the discovery of ring wells from the district for the second time established these facts.