Big names including Roger Federer, Rafael Nadal and Novak Djokovic were scheduled to play their opening matches at the clay-court tournament, but will have to wait until Thursday now.
Federer was set to make his first appearance at the event since 2016 against Portugal’s Joao Sousa, eight-time Rome champion Nadal was due to play France’s Jeremy Chardy, and Djokovic was to go up against Canadian Denis Shapovalov.
Also, top-ranked Naomi Osaka and American world number eight Sloane Stephens were scheduled to play.
Osaka was to take on Slovakia’s Dominika Cibulkova, while Sloane was to play Britain’s Johanna Konta.
Postponed games will now be included in Thursday’s day session, which will be split into two parts.
Better weather in the Italian capital is forecast for Thursday and Friday.