In 1802, the British began the Great Trigonometric Survey of India to fix the locations, heights, and names of the world's highest mountains. Starting in southern India, the survey teams moved northward using giant theodolites, each weighing and requiring 12 men to carry, to measure heights as accurately as possible. They reached the Himalayan foothills by the 1830s, but Nepal was unwilling to allow the British to enter the country due to suspicions of their intentions. Several requests by the surveyors to enter Nepal were turned down.