Seleucid Empire was created in 312.

The Romans never conquered the Seleucid Empire.

Antiochus Epiphanes.

After the death of Alexander the Great, his generals split his empire among themselves. One of these generals was Seleucus, received the Eastern part of the empire. He was the first member of the Seleucid Dynasty. The Seleucid Empire, and the dynasty, survived until 63 BC, when what was left of the empire became part of the Roman province of Syria.

The two best are the Romans and the Seleucid's.