The Colosseum and the Baths of Caracalla will open until midnight every Saturday night from 21 August until 23 October.
An agreement has also been reached with the unions to open the House of Livia on the Palatine and the Temple of Romulus in the Roman Forum during the day as from 21 August. Both sites are usually closed to the public.
However the opening of additional parts of the Colosseum, which was announced earlier this year, has now been put off until the beginning of September.
The delays are the result of difficulties with staff about shifts and overtime pay.