 The state is also the main administrative centre of many Indian defence aero-space and research labs like Bharat Dynamics Limited, Defence Metallurgical Research Laboratory, Defence Research and Development Organisation and Defence Research and Development Laboratory.The cultural hearts of Telangana, Hyderabad, and Warangal, are noted for their wealth and renowned historical structures – Charminar, Qutb Shahi Tombs, Paigah Tombs, Falaknuma Palace, Chowmahalla Palace, Warangal Fort, Kakatiya Kala Thoranam, Thousand Pillar Temple and the Bhongir Fort in Yadadri Bhuvanagiri district.The historic city Golconda in Hyderabad established itself as a diamond trading center and, until the end of the 19th century, the Golconda market was the primary source of the finest and largest diamonds in the world.