Banks had been tipped to join the club last month and the Italian club confirmed it yesterday with a statement on its website.
The club had signed the Highlanders utility back and the move will further a career for Banks that began with Buller and continued with club rugby in Russia.
A West Coaster, Banks (26) has had an injury-disrupted season with rib damage and a sore hamstring.
An inability to get a starting spot with the Highlanders would have played a part in Banks heading offshore.
The No10 jersey is held down by All Black first five-eighth Lima Sopoaga.
Banks holds many point-scoring records for his province, Tasman, and has an accurate boot, which has been a big part in Tasman's success over the past few years.
Grant (28) has signed for the union for one year, having spent nearly three years overseas.
Grant has played 57 games for Otago and captained the side when it won the Ranfurly Shield in 2013.
He initially left to play for French club Montpellier as an injury replacement at the end of the Otago season in 2013.
Grant then moved to play for Nottingham in the English Championship, which is the next tier down from the Premiership.
The No8 said in a statement yesterday it was tough deciding between staying in England and coming back, but he was glad he had returned.
He would rest up for the next couple of weeks and then return to the field.
A South Otago High School product and a former University A forward, Grant had not yet decided what club team he would play for.