Answer: Constantine built the new capital city
Diocletian split the empire into east and west
Hadrian traveled the empire and built the wall in Britain
Explanation: Constantine built the new capital of the Roman Empire - Constantinople, and conveyed the capitol from Rome in 330 AD. This marked the new capital, "New Rome".
Diocletian ruled from 284 to 305 AD, stabilized the Roman Empire by overcoming the crisis of the third century. He divided the empire into two parts in 284 AD, as one of his first orders when he became an emperor, where he ruled Eastern part, and the western part was ruled by Maximian.
Emperor Hadrian ruled from 117 to 138 AD, during his travels through Britain, decided and ordered the construction of a wall in order to "separate the Romans from the barbarians."