Campo del Cielo refers to a group of iron meteorites and the area in Argentina where they were found. The site straddles the provinces of Chaco and Santiago del Estero, located north-northwest of Buenos Aires, Argentina and approximately southwest of Asunción, Paraguay. The crater field covers and contains at least 26 craters, the largest being . The craters are estimated to be four to five thousand years old. They were reported to the general public in 1576, but were already well-known by aboriginal peoples. The craters and surrounding areas contain many fragments of an iron meteorite. In total, approximately 100 tonnes of fragments have been recovered, the most of any meteorite find. The two largest fragments, the 30.8-tonne Gancedo and 28.8-tonne El Chaco, are among the heaviest single-piece meteorite masses recovered on Earth, following the 60-tonne Hoba meteorite and a 31-tonne fragment of the Cape York meteorite. History In 1576, the governor of a province in northern Argentina commissioned the military to search for a huge mass of iron, which he had heard that natives used for their weapons. The natives claimed that the mass had fallen from the sky in a place they called Piguem Nonralta, which the Spanish translated as Campo del Cielo ("Field of heaven (or the sky)"). The expedition found a large mass of metal protruding out of the soil and collected a few samples, which were described as being of unusual purity. The governor documented the expedition and submitted the report to the General Archive of the Indies in Seville, Spain, but it was quickly forgotten and later reports merely repeated the native legends. Following the legends, in 1774 Don Bartolomé Francisco de Maguna rediscovered the iron mass which he called el Mesón de Fierro ("the Table of Iron"). Maguna believed that the mass was the tip of an iron vein. The next expedition, led by Rubin de Celis in 1783, used explosives to clear the ground around the mass and found that it was likely a single stone. Celis estimated its mass as 15 tonnes and abandoned it as worthless. He believed that it had formed by a volcanic eruption, rather than being a meteorite. However, he sent samples to the Royal Society in London and published his report in the Philosophical Transactions of the Royal Society. Those samples were later analyzed and found to contain 90% iron and 10% nickel; they were assigned