The Campo del Cielo refers to a group of iron meteorites or to the area where they were found situated on the border between the provinces of Chaco and Santiago del Estero, 1,000 kilometers (620 mi) northwest of Buenos Aires, Argentina. The crater field covers an area of 3×20 kilometers and contains at least 26 craters, the largest being 115×91 meters. The craters' age is estimated as 4,000–5,000 years. The craters, containing iron masses, were reported in 1576, but were already well known to the aboriginal inhabitants of the area. The craters and the area around contain numerous fragments of an iron meteorite. The total weight of the pieces so far recovered exceeds 100 tonnes, making the meteorite the heaviest one ever recovered on Earth. The largest fragment, consisting of 37 tonnes, is the second heaviest single-piece meteorite recovered on Earth, after the Hoba meteorite.