Home > Bengal History, General > Great Trigonometrical Survey (GTS) Towers

Great Trigonometrical Survey (GTS) Towers

Great Trigonometrical Survey (GTS) Towers

A compilation of GTS Towers of West Bengal

The Great Trigonometrical Survey (GTS), started in 1800 and continued over half a century. It is often hailed as one of the most stupendous work in the history of science. The Great Arc (780 E Longitude) was the backbone of the survey and the 1600 miles of inch perfect survey was the longest measurement of earth surface ever to have been attempted.

Collage of GTS Towers

Collage of GTS Towers
Left – right: Paikpara, Akanpur, Bhalki, Bhola and Sukchar

Willam Lambton, an endearing genius, conceived the idea; George Everest, an impossible martinet, took it forward. The half a century long project involved equations more complex than any in the pre – computer age. It was also the most perilous project of its time, killing more men than any contemporary wars. Malaria wiped out whole survey parties, tiger and scorpions took their toll.

Index Chart of Great Trigonometrical Survey of India (1870), Top right: William Lambton, Bottom Left: George Everest

Index Chart of Great Trigonometrical Survey of India (1870), Top right: William Lambton, Bottom Left: George Everest (Source:Surveying Empires and Wikimedia Commons)

Unshaken by the dangers an intrepid band of surveyors carried on through the dense rain forest of South India to the perennial snow fields of Himalayas. With instrument weighing half a ton, their observations were often carried out from flimsy platforms ninety feet above ground or from mountain peaks enveloped in blizzards.

James Prinsep's sketch of measurement of base line of Calcutta longitude, 1831

James Prinsep’s sketch of measurement of base line of Calcutta longitude, 1831 (Source: Wikimedia Commons)

Calcutta formed the institutional base of GTS under George Everest in 1820 – 30. From Calcutta four series of triangulation spread their wings in the north, south east and west directions. The western wing travelled all the way across the northern part of the country to meet the Great Arc.

Present day google map showing the Calcutta Longitude base line

Present day google map showing the Calcutta Longitude base line

In this low lying and relatively flat region of eastern India, it was necessary to build brick towers to provide a stable elevated platform from where the survey work can be conducted. So it resulted in construction of massive 75 feet brick towers, which dot the Bengal landscape even to this day. A 6 mile stretch along the Barrackpur Road (BT Road) was uses as the base line. Towers towering were built at either end of the base line.

Write up on Calcutta base line towers. Left - right: Paikpara (english and Bengali and Sukchar (English and Bengali)

Write up on Calcutta base line towers
Left – right: Paikpara (English and Bengali) and Sukchar (English and Bengali)

Today locally known as Girja (Church), Batighar (Lighthouse) and Mancha (Elevated platform) and are also often regarded as watch towers to keep watch on invading armies. The GTS towers today from an important source of ethnography studies and these locally collected stories form an interesting intangible heritage of the otherwise tangible GTS towers.

1. Paikpara

GTS Tower, Paikpara

GTS Tower, Paikpara

Google map location

Station No.: LXXXV

Observed on: 1832, 1844-45 and 1848

The tower marks the southern end the base line of the Calcutta longitude series. The tower was built by Parker and towered to a height of about 75 feet.

It has a truncated pyramidal structure with the base base measuring 17 feet square and the top measuring 13 feet square.

The tower is presently a property of Public Works Department (PWD) who gave the century old tower a new makeover of a milk white paint. A brief history of the tower and GTS is inscribed on the outer wall of the tower in English and Bengali.

A few decades ago the tower spotted an advertisement of the popular antiseptic cream Boroline and was popularly known as the Boroline Tower

Today the tower stands at the junction of the BT Road and the lockgate flyover and just south of Chiria More. The tower is structural in sound conditions and the gates are always locked.

2. Sukchar

GTS Tower, Sukchar

GTS Tower, Sukchar

Google map location

Station No.: LXXXII

Observed on: 1832, 1845, 1848 and 1869

The tower marks the northern end the base line of the Calcutta longitude series and is almost a exact replica of its southern counterpart..

This too is owned by the PWD and spots a milk whit exterior with the brief history of GTS written in English and Bengali.

It is locally known as Girja (literally meaning Church). It stands at the crossing of BT Road and Ekford, which also is known as Girja More.

3. Bhola

Bhola 1

GTS Tower, Bhola

Google map location

Station No.: LXXX

Observed on: 1832, 1845, 1848 and 1869

Again a truncated pyramidal tower, towering approximately to a height of 75 feet. The plaster have long peeled off exposing the bricks measuring 24cm in length, 10.5cm wide, and 6 cm in height.

The tower has two arched gateways on opposite side and there are four elongated rectangular windows on each side.

Locals opine that the tower served as a watch tower for keeping an eye on the invading Marathas (Bargis). Today the tower is located on the Howrah – Tarkeshwar line just beyond Kamarkundu station. People traveling from Howrah can spot the tower on the right just beyond the Kamarkundu station.

4. Akanpur

Bhola 1

GTS Tower, Akanpur

Google map location

Station No.: LXXVI

Observed on: 1832 and 1869

The tower was built by Joshep Olliver in 1825 – 30 and then the first observation taken in 1832.

It collapsed soon after and during the revision of Calcutta longitude in 1866 – 67 it had to be reconstructed for the 1869 observation.

This also is a truncated pyramidal structure of about 45 feet high. It has arched headway windows on all four sides. Each side have three elongated rectangular windows on each side. The base has two arched doorways on opposite side. locals refer to it as Girja

5. Samalia

GTS Tower, Samalia

GTS Tower, Samalia

Google map location

Station No.: LXXXVII

Observed on: 1848

The 63 feet high truncated pyramidal tower lies at the Samalia village located on the Thakurpukur – Bakhrahat Road.

According to the 1880 report “he station is inaccessible during the rains, except by boats.”

Today locals call know it as Batighar (literally meaning Light House). It is reached by a long winding path from the main road.

Large portions of the structure collapsed in 2012 and presently one of the walls have entirely collapsed. The ruined structure lies in the midst of a agricultural field owned by the Naskar Family. They stay in the shadows of the tower with the constant fear that it could collapse on there residence any day.

6. Bhalki

GTS Tower, Bhalki

GTS Tower, Bhalki

Google map location

Station No.: LXVIII

Observed on: 1831 and 1868

Bhalki or Valki houses one of the most unique GTS Towers of the Calcutta longitude series. The 35 feet tower has no walls and has the four L shaped structures at the four corners.

At the centre is another brick pillar with a central vertical hole. At the base of the central pillar is a passageway and a dip pit approached by arched gateways on either side. The pit is covered with a iron grill.

Today Bhalki or Valki is a popular tourist spot attracting tourist from Kolkata and other nearby towns. The locals refer it as Valki Machan or Bhalki Machan and believed to be used by the local landlord for hunting Bear (Bengali word for bear is Bhaluk) and hence the name Valki Machan or Bhalki Machan.

Also see:

Semaphore Connect

the towers have been built earlier in the century as part of a primitive, pre-elctric telegraph system by which messages, preferably short ones, could be flashed up-country from tower to tower. Everest had himself worked on the telegraph towers before being posted to the Great Trigonometrical Survey in 1818…

John Keay, The Great Arc

Collage of Semaphore Towers

Collage of Semaphore Towers

The optical telegraph or Semaphore Towers required some modification for survey and several of them were modified and were used in GTS. The Semaphore towers with its truncated cone shape can easily be distinguished from the GTS towers.

More on:


  1. John Keay, The Great Arc
  2. Synopsis of the result of the operation of The Great Trigonometrical Survey of India, Volume XII
  3. Official website of Surveying Empires

Special Thanks: Special thanks to Keith Lilley, Satish Kumar (Belfast University) and Rajat Sanyal (Calcutta University) and the entire Surveying Empire team.

  1. January 20, 2021 at 12:59 AM

    Another fascinating post!!! Great research, well written and excellently illustrated!! First Class!!!

  2. January 20, 2021 at 10:50 AM

    This is the first article that I have seen by you. It’s brilliant and totally fascinating! We are depriving children of these kinds of knowledge in their geography and history classes under syllabi designed by the most unimaginative academics. It’s the Great Deprivation!

    Thank you for this article. I will read others in your blog soon. I look forward to using several of them in my teaching.

  3. Bikram Jeet
    January 20, 2021 at 10:07 PM

    Wonderful information. So much history just in plain sights.Thanks for sharing.

  4. Pritam Das
    February 25, 2021 at 10:30 PM

    I saw this type of tower in Berugram road, Purba Bardhaman

    • February 25, 2021 at 10:33 PM

      Can you please share more details of the location

  5. Rammyani
    July 13, 2021 at 1:11 PM

    Valuable information. Thank you for enlightening.

  6. Tapan Kumar Mukherjee
    February 18, 2022 at 5:39 PM

    This is a most interesting article. The images of GTS towers displayed in the article closely resemble that of the image of the tower in the background of the photograph of James Prinsep Calcutta Base Line. The image of Bhalki Machan is a solitary exception and is unlike other images. May I suggest an alternative theory apart from the commonly accepted theory of GTS tower or Bear Hunting tower. The underground pit in the middle indicates that there might be an underground tunnel that was used as an escape route after observing the approach of enemy at a distance from the top of the watch tower. It is said that the underground tunnel is connected to the fort of Bhabani Pathak in nearby Durgapur, an historical figure depicted in the novel Debi Choudhurani by Bankim Chandrw Chatterjee. This possibility has hitherto remained unexplored. Academics may kindly look into this aspect.

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