Quick answer
The ancient tanks of the Cultural Triangle are man-made reservoirs, called wewa in Sinhala, built from roughly the 4th century BC onwards to store monsoon rain for the dry zone's rice fields. Anuradhapura's Basawakkulama, Tissa Wewa and Nuwara Wewa supplied the first capital; Kala Wewa fed it through the 87-kilometre Jaya Ganga canal; Minneriya and Parakrama Samudra watered Polonnaruwa. Many still irrigate fields today, and Minneriya and Kaudulla tanks draw the famous elephant gathering from roughly July to September.
Key takeaways
- Basawakkulama in Anuradhapura, traditionally dated to around the 4th century BC, is regarded as one of the oldest surviving reservoirs in Sri Lanka.
- The Jaya Ganga canal carried water roughly 87 kilometres from Kala Wewa to Anuradhapura on an extremely gentle gradient.
- The bisokotuwa, a valve pit set into a tank's embankment, controlled outflow and is one of ancient Sri Lanka's key engineering inventions.
- Parakrama Samudra, built by Parakramabahu I in the 12th century, is a series of connected tanks covering over 20 square kilometres beside Polonnaruwa.
- Minneriya tank, attributed to King Mahasena in the 3rd century AD, draws hundreds of elephants to its shores in the dry season.
What a tank is
A tank in the Cultural Triangle is a reservoir made by building an earth embankment, called a bund, across a shallow valley to trap monsoon rain. The dry zone receives most of its rain in a few months, roughly October to January, so storing it was the only way to grow rice through the rest of the year.
Tanks range from small village wewas, a few hundred metres across, to vast royal reservoirs such as Parakrama Samudra. Smaller tanks were often linked in cascades, each one overflowing into the next down the valley, so water was used again and again before it reached the sea.
The village pattern of tank, paddy field and temple, called wewai, dagabai, gamai, pansalai in a Sinhala saying, still defines much of the Cultural Triangle landscape.
- →Wewa: a tank or reservoir.
- →Bund: the earth embankment that holds the water.
- →Cascade: a chain of linked village tanks.
- →Ela: a canal carrying water between tanks.
The engineering
Ancient Sri Lankan engineers solved hard problems in the Cultural Triangle with simple materials. The greatest challenge was releasing water from a full tank without the pressure tearing the bund apart. Their answer was the bisokotuwa, a stone-lined valve pit set into the embankment, which slowed and controlled the flow. It appears from around the 3rd century BC.
Canals were just as impressive. The Jaya Ganga carried water roughly 87 kilometres from Kala Wewa to Anuradhapura's tanks, falling only a few centimetres per kilometre over much of its length. Surveying that precisely without modern instruments still impresses engineers.
- →Bisokotuwa: the valve pit that controlled outflow.
- →Spillways: stone channels to release overflow safely.
- →Jaya Ganga: an 87-kilometre canal on a very gentle gradient.
- →Cascades: thousands of linked village tanks.
The great royal tanks
Several Cultural Triangle kings are remembered above all as tank builders. King Mahasena, in the 3rd century AD, is credited with Minneriya and many others, and is still honoured locally as a god of the tanks. King Dhatusena built Kala Wewa in the 5th century, before his son Kashyapa built Sigiriya.
Parakramabahu I of Polonnaruwa, who reigned from 1153 to 1186, is said to have declared that not a single drop of rain should reach the sea without first serving people. Parakrama Samudra, his sea of Parakrama, lies beside the ruins today.
- →Tissa Wewa and Nuwara Wewa: Anuradhapura's main tanks.
- →Kala Wewa: King Dhatusena's 5th-century reservoir.
- →Minneriya: attributed to King Mahasena, 3rd century AD.
- →Parakrama Samudra: Parakramabahu I's 12th-century reservoir.
Where first-time visitors can see them
First-time visitors see tanks everywhere in the Cultural Triangle, but a few are worth a deliberate stop. In Anuradhapura, Tissa Wewa at sunset, near Isurumuniya, is beautiful, and the bund of Nuwara Wewa gives wide views. In Polonnaruwa, the Parakrama Samudra bund runs right beside the ruins and is lovely in the late afternoon.
Minneriya and Kaudulla tanks are where the elephant gathering happens, seen on jeep safaris from Habarana. Kala Wewa sits beside the Avukana Buddha. Around Sigiriya, the Sigiriya tank and smaller village tanks are crossed on catamaran rides as part of village tours.
Lankan Stays & Trails often builds a tank sunset into the first or last evening of a Cultural Triangle stay, because the light, birds and fishermen make a calm end to a hot day.
Tanks today
Many of the Cultural Triangle's ancient tanks still irrigate rice fields, restored and enlarged in the 20th century. They also support fishing, wildlife and the water supply of towns. The tank cascade system has been recognised by the Food and Agriculture Organization as a Globally Important Agricultural Heritage System.
Tanks are also wildlife habitats. Egrets, cormorants, pelicans, painted storks and kingfishers gather along their edges, crocodiles bask on the banks, and elephants come down to drink in the dry season.
- →Irrigation: thousands of hectares still watered.
- →Fishing: tilapia from the tanks is common in local curries.
- →Wildlife: birds, crocodiles and elephants.
Frequently asked questions
What is a tank in Sri Lanka?
A tank is a man-made reservoir, called wewa in Sinhala, built by damming a shallow valley with an earth bund to store monsoon rain for irrigation. The dry zone holds thousands, many built between the 4th century BC and the 12th century AD and still in use today.
Who built the ancient tanks of Sri Lanka?
Kings and villagers together. Kings such as Mahasena, Dhatusena and Parakramabahu I built the great royal reservoirs, while village communities built and maintained thousands of small tanks linked in cascades. The system developed over roughly 1,500 years.
What is the oldest tank in Sri Lanka?
Basawakkulama in Anuradhapura, also called Abhaya Wewa, is traditionally dated to around the 4th century BC and is often described as the oldest surviving reservoir in Sri Lanka. Tissa Wewa nearby dates to roughly the 3rd century BC.
What is the Jaya Ganga canal?
The Jaya Ganga is an ancient canal running roughly 87 kilometres from Kala Wewa to the tanks of Anuradhapura. Built in the 5th century, it falls very gently over much of its length, an impressive feat of surveying still admired by engineers.
Where can I see ancient tanks near Sigiriya?
The Sigiriya tank lies beside the rock, and village tanks around Sigiriya and Habarana are crossed on catamaran rides during village tours. Minneriya and Kaudulla tanks, about 30 to 45 minutes away, host the elephant gathering roughly July to September.
Is Parakrama Samudra worth visiting?
Yes, as part of a Polonnaruwa visit. The bund runs beside the ruins and the royal palace, and a late-afternoon stop gives wide views over the water, birds and fishermen. It costs nothing and makes a calm end to a morning in the ancient city.
Do the ancient tanks still work?
Many do. Restored in the 20th century, tanks such as Minneriya, Kala Wewa and Parakrama Samudra still irrigate rice fields, supply towns and support fishing. Some smaller village tanks have silted up, but cascade restoration projects continue.