This is a design for a panel to decorate a temporary theatre for a performance of the comedy 'La Talanta' by Pietro Aretino (1492 - 1556). Vasari organized the decorations and it was performed during the Venice Carnival of February 1542. Other panel designs are in collections in Paris and Berlin.
The gods shown here represent Lake Garda and the small rivers of Mincio and Ticino which flow from the Lake to the River Po. The Po fed and fertilised the plain south of Venice; hence the inclusion of cornucopiae overflowing with water and fruit.