The pre-Hispanic ruins of Mexico City’s Templo Mayor archaeological site suffered minor but reparable damage when large sections of a corrugated roof structure meant to protect them collapsed during a hailstorm., authorities said Friday. The Culture Department said the steel-framed, lightweight roof fell under the weight of hail and high winds Thursday night. The National Institute of Anthropology and History called the amount of hail “unheard of.” The roofing fell on only part of the block-long site and neither the sites frescos nor carvings were damaged, the institute said. It said a plaster floor area was hit, though it can be restored. The Culture Department said that “the damage to the pre-Hispanic structure is minor, recoverable and can be restored,” but did not say how that would be done. The institute said a new roof would be erected at the site. The twin temples and adjacent buildings just off Mexico Citys main plaza were largely razed by the Spaniards after their 1521 conquest of Mexico. But large lower sections of the platforms remained hidden under subsequent building layers, and were re-excavated starting in 1978. The roof also made touring the ruins more pleasant for visitors. One guard was injured in the roof collapse, and he was listed in stable condition at a hospital.