Italy issued hot weather red alerts for 16 cities on Sunday, with meteorologists warning that temperatures will hit record highs across southern Europe in the coming days.
On the Spanish island of La Parma, meanwhile, at least 4,000 people had to be evacuated as a forest fire burned out of control, authorities said.
Spain, Italy, and Greece have been experiencing scorching temperatures for several days already, damaging agriculture and leaving tourists scurrying for shade.
But a new anticyclone dubbed Charon, who in Greek mythology was the ferryman of the dead, pushed into the region from North Africa on Sunday and could lift temperatures above 45 Celsius (113 Fahrenheit) in parts of Italy early this week.
"We need to prepare for a severe heat storm that, day after day, will blanket the whole country," Italian weather news service Meteo.it warned on Sunday.
"In some places ancient heat records will be broken."
Many attractions will be closed
Greece closed the ancient Acropolis during the hottest part of the day on Friday to protect tourists.
Italy's Health Minister Orazio Schillaci said authorities were keeping a close eye on Rome and urged people to take care.
"Going to the Colosseum when it is 43C (109.4F) is not advisable, especially for an elderly person," he told Il Messaggero newspaper on Sunday, saying people should stay indoors during the hottest part of the day, between 11 a.m. and 6 p.m.
Besides the Italian capital, health alerts were in place from the central city of Florence to Palermo in Sicily and Bari, in the southeast of the peninsula.
In Spain, forecasters warned of the risk of forest fires and said that it would not be easy to sleep during the night, with temperatures unlikely to fall below 25C (77F) across the country.
The heatwave will intensify from Monday, with temperatures reaching 44C (111.2F) in the Guadalquivir Valley near Seville in the south of the country, forecasters predicted.
Europe's highest recorded temperature of 48.8C (119.8F), registered in Sicily two years ago, could be exceeded in the coming days, notably on the Italian island of Sardinia, meteorologists have said.
Remember to stay hydrated and not spend too long in the sun.