Greek is an Indo-European language, the sole surviving descendant of the Hellenic sub-family. Although it split off from other Indo-European languages around the 3rd millennium BCE (or possibly before), it is first attested in the Bronze Age as Mycenaean Greek. During the Archaic and Classical eras, Greek speakers wrote numerous texts in a variety of dialects known collectively as Ancient Greek. In the Hellenistic era, these dialects underwent dialect levelling to form Koine Greek which was used as a lingua franca throughout the eastern Roman Empire, and later grew into Medieval Greek. For much of the period of Modern Greek, the language existed in a situation of diglossia, where speakers would switch between informal varieties known as Dimotiki and a formal one known as Katharevousa. Present-day Modern Standard Greek is largely an outgrowth of Dimotiki, with some features retained from Katharevousa.