The Roman Empire began with the crowning of Gaius Octavian Thurinus in 31 B.C. and fell to the German Goths in A.D. 476, for a total of 507 years. The Byzantine Empire, Rome's eastern half, did not fall until the Ottoman Turks conquered Constantinople in 1453.
Rome itself lasted over 1,200 years, first as a kingdom during the eighth century B.C. In 507 B.C., King Lucius Tarquinius Superbus was overthrown by a citizens' revolt, and the Roman nobility declared the growing nation to be a republic governed by a senate and two or three consuls.
Caesar was one of the last three consuls. When the consul Crassus died, Pompey, the consul in Rome, declared himself sole ruler. Caesar rebelled and defeated him, claiming sole Roman leadership for himself in 32 B.C. The consul system was irretrievably broken, and Rome became an empire.