Science News

Submerged ancient Indian harbour may have been design inspiration for Neapolis, Alexandria

K. S. Jayaraman

doi:10.1038/nindia.2020.133 Published online 31 August 2020

Researchers have discovered an ancient harbour-like structure under sea, buried at a depth of about 80 metres off the Bay of Bengal1.

The researchers from Bharathidasan University (BU) in Tiruchirappalli have traced the harbour – roughly 11 km long and 2 km wide – about 25km east of Poompuhar on the Tamil Nadu coast1.

The discovery of the nearly 15,000 year old structure points to a past of  bustling maritime trade in these parts, according to Somasundaram Ramasamy, a professor in the department of remote sensing at BU and coordinator of the project. The Rs 90-million project is part of India’s national mission to digitally reconstruct underwater heritage sites.

At the mouth of one of the oldest deltas of river Cauvery, Poompuhar or Keveripoompattinam was a port city established by the Chola dynasty around 2000 years ago. The city had trade linkages with major parts of Asia and adjoining continents. "But around 1000 years ago it vanished from the maritime history of the world leaving several mysteries behind,” Ramaswamy told Nature India.

The researchers set out to unravel the mystery using ocean bathymetry and past sea level data. Earlier, they had discovered that the original Poompuhar (Poompuhar-1) existed about 30-km east of today's Kaveripoompattinam about 20,000 years ago and had shifted location four times due to continuous sea level rise and changing coastline2. "The earlier three were swallowed one after the other by the sea forcing people to shift further westerly towards the new coast and establish the present-day Kaveripoompattinam at the mouth of river Cauvery," Ramasamy says.

The latest study1 was carried out to look for any submerged structures between the original Poompuhar and the present coast using digital elevation model (DEM) and digitally processed multi-beam echo sounder (MBES) data. Besides the harbour structure, the study discovered a network of canals for the movement of ships and boats. This, and associated structures like breakwaters (to reduce coastal erosion) and sea walls (to protect the harbour from waves and storm surges) show that "besides the construction technology, our ancestors were aware of marine dynamics and the environment too", Ramasamy says.

"These might have been constructed by the ancient people around 11,000–15,000 years ago, as these are located in one of Cauvery’s oldest deltas, which fall in between the shorelines of the above period,” he says.

The pattern and layout of the ancient harbour structure found in Poompuhar-1 is similar to several harbours around the world – like Neapolis in Greece, Alexandria in Egypt and King Louis in Mauritius. "But all of them are much younger – only 6000-2000 years old – compared to the structure found in Poompuhar-1 that is about 15,000 years old", says Ramasamy.

The maritime activities of Poompuhar might have been much older and such construction technology might have been transferred from Poompuhar to other parts of the world," he suggests. Further studies using advanced tools like single beam and MBES data, underwater profiler survey, and optical and sonar photography are needed to conclusively prove these aspects.


References

1. Ramasamy, SM. et al. Detection of submerged harbour using GEBCO and MBES data, in the offshore region of ancient port city Poompuhar, South India. Curr. Sci. 119, 526-533 (2020) Article

2. Ramasamy, SM. et al. Coordinates and chronology of the ancient port city of Poompuhar, South India. Curr. Sci. 112, 1112-1114 (2017) Article