Iran is marking the 40th anniversary of the Islamic Revolution that toppled the US-backed shah, overturned 2,500 years of monarchical rule, and brought hardline Shiite clerics to power. The anniversary begins every year on February 1 – the day Ayatollah Ruhollah Khomeini in 1979 returned from France after 14 years in exile to become the supreme leader of the Islamic Republic of Iran. Sirens rang out across the country on Friday, AP reports. The 10-day anniversary festivities, known as the “Ten Days of Dawn,” end on February 11, the date Shah Mohammad Reza Pahlavi’s government collapsed.