He completed the Colosseum
One of the most interesting facts about Domitian is that he completed the Colosseum. The Colosseum is an oval amphitheater located in Rome, Italy, immediately east of the Roman Forum. It is the largest ancient amphitheater ever erected and, despite its age, the largest standing amphitheater in the world today. Construction began in 72 during the reign of Emperor Vespasian (r. 69-79 AD) and was completed in 80 AD under the reign of his successor and heir, Titus. During Domitian's rule, additional changes were enacted (r. 81–96). The Flavian dynasty was named after the three emperors who supported the project, and the amphitheater was named after them.
The structure was later rebuilt by Vespasian's younger son, the newly proclaimed Emperor Domitian, who built the hypogeum, a system of tunnels used to keep animals and slaves. He also constructed a gallery on the Colosseum's roof to boost seating capacity. The arena was 83 by 48 meters (272 by 157 feet / 280 by 163 Roman feet). It consisted of a hardwood floor covered in sand (harena or arena is the Latin word for sand) that encased a complex underground construction known as the hypogeum (literally meaning "underground"). Emperor Domitian ordered the construction of the hypogeum, which was not part of the original design. Early in the Colosseum's history, however, the construction of the hypogeum at Domitian's request put an end to the practice of flooding, and hence to naval battles.
