Culture of ancient Rome
The Roman Empire, at its height (c. 117 CE), was the most extensive political and social structure in western civilization. By 285 CE the empire had grown too vast to be ruled from the central government at Rome and so was divided by Emperor Diocletian into a Western and an Eastern Empire. The Roman Empire began when Augustus Caesar became the first emperor of Rome (31 BCE) and ended, in the west, when the last Roman emperor, Romulus Augustulus, was deposed by the Germanic King Odoacer (476 CE). In the east, it continued as the Byzantine Empire until the death of Constantine XI and the fall of Constantinople to the Ottoman Turks in 1453 CE. The influence of the Roman Empire on western civilization was profound in its lasting contributions to virtually every aspect of western culture.
Holy Roman Emperor
From an autocracy in Carolingian times (AD 800–924) the title by the 13th century evolved into an elected monarchy chosen by the prince-electors.
Various royal houses of Europe, at different times, became "de-facto" hereditary holders of the title, notably the Ottonians (962–1024) and the Salians (1027–1125). Following the late medieval crisis of government, the Habsburgs kept possession of the title without interruption from 1440–1740. 
The final emperors were from the House of Lorraine (Habsburg-Lorraine), from 1765–1806.
The Holy Roman Empire was dissolved after the defeat at Austerlitz by emperor Francis II, who continued to rule as Austrian emperor.