The Great Trigonometrical Survey (GTS)
This was one of the most stupendous human endeavors in history. Proposed by British infantry officer William Lambton and later completed by George Everest, the project aimed to measure the entire Indian subcontinent with scientific precision.
They set out to measure the Great Arc of the Meridian from the southern tip of India to the Himalayas. Surveyors used massive "Great Theodolites" weighing over 1,000 pounds, dragging them across malarial swamps, jungles, and deserts. It took nearly 70 years, cost many lives, but resulted in the first highly accurate maps of India and led to the discovery and measurement of the world's highest peaks, including Peak XV (later named Mount Everest).