The four Roman Emperors named in the crossword are OTTO, Augustus, Nero, and Tiberius. OTTO was a German king who reigned from 936 to 973 and is known for his successful military campaigns. Augustus was the first Roman Emperor and ruled from 27 BC to 14 AD. He was the grandnephew of Julius Caesar and is known for establishing the Pax Romana. Nero was the fifth Roman Emperor and ruled from 54 to 68 AD. He is known for his extravagance and cruelty. Tiberius was the second Roman Emperor and ruled from 14 to 37 AD. He is known for his military successes and for his reputation as a recluse.