My new Ancient Roman coin

My favorite History teacher kindly gave my this coin.  We don't know much about the coin itself.  One side depicts the head of Emperor Domitian of Rome, and for the other side, we don't know entirely what is depicted. This is what we do know: this coin was minted under the rule of Emperor Domitian. Domitian ruled under the Flavian dynasty. His father, Vespasian, was a famous general and excellent strategist.  His older brother, Titus was another general, and is remembered to this day by the Arch of Titus.  This dynasty is also famous for building the Coliseum, or at the time, the Flavian Amphitheater.