In the 1990s strange events started to happen around Rome. Beginning in 1991 and lasting for three years, a series of earthquakes shook the ancient city. Then scientists noticed something really odd: the surrounding hills were slowly becoming taller.
Moreover, in September 1999, 29 cows were found dead on the hillsides of Colli Albani. On closer investigation, moreover, it was discovered that carbon dioxide had leaked from the ground and asphyxiated the animals. Then two years later, eight sheep died in the same circumstances.