The Mediterranean nation is forecasting temperatures over 40 degrees Celsius (104 degrees Fahrenheit) in the coming days, according to the National Meteorological Service.
"From Tuesday, August 3, to Thursday, August 5, archaeological sites in the open air will be closed from 12:00 [local time, 09:00 GMT] to 17:00 for the safety of visitors and employees due to high temperatures," the ministry said in a statement.
With the country's power system being overloaded from the heat, Prime Minister Kyriakos Mitsotakis urged people earlier on Monday to reduce the use of electricity as much as possible, especially in the daytime from 1 p.m. to 3 p.m., to avoid blackouts.
Recent days have brought Greece its worst heatwave since 1987 when temperatures reached 43 degrees Celsius for several days and 1,300 people lost their lives due to the extreme weather. On Monday and Tuesday, the temperature is expected to reach 44-46 degrees Celsius on the mainland.