Rome has a classic Mediterranean climate. Summers (June–August) are very hot and dry at 30–34°C, with August the peak tourist month despite the heat (and many locals leaving). Spring (April–May) and autumn (September–October) are ideal: 18–24°C, lower crowds, and the city at its most pleasant.
Winters (December–February) are mild by European standards (8–13°C) with some rain — much lower crowds and better hotel prices. Christmas in Rome is atmospheric, with nativity scenes (presepi) throughout the city. July–August heat is manageable with early morning sightseeing, long afternoon rest, and evening recovery.