Dolphins were a popular motif in Roman art, depicted in bronze, as well as mosaics and frescoes. They also appear frequently in mythology, often helping Classical heroes such as Theseus, as well as being associated with gods such as Bacchus, Apollo, Venus, and Cupid, who is often shown riding on a dolphin.
For more information about the meanings of animals in Roman art, see our relevant blog post: Animal Symbolism in Roman Art.