Greek is an Indo-European language, the sole surviving descendant of the Hellenic sub-family. Although it split off from other Indo-European languages before 2000 BC, 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. Proto-Greek The Proto-Greek language was the most recent common ancestor of all Greek dialects. Proto-Greek split off from its nearest Indo-European relatives some time before 2000 BC, though it is unknown whether the characteristic Greek sound-changes occurred within the Greek peninsula or if Proto-Greek speakers themselves migrated into Greece. Mycenaean Greek The first known script for writing Greek was the Linear B syllabary, used for the archaic Mycenaean dialect. Linear B was not deciphered until 1953. After the fall of the Mycenaean civilization during the Bronze Age collapse, there was a period of about five hundred years when writing was either not used or nothing has survived to the present day. Since early classical times, Greek has been written in the Greek alphabet. Ancient Greek dialects In the archaic and classical periods, there were three main dialects of the Greek language: Aeolic, Ionic, and Doric, corresponding to the three main tribes of the Greeks, the Aeolians (chiefly living in the islands of the Aegean and the west coast of Asia Minor north of Smyrna), the Ionians (mostly settled in the west coast of Asia Minor, including Smyrna and the area to the south of it), and the Dorians (primarily the Greeks of the coast of the Pelopennesus, for example, of Sparta, Crete and the southernmost parts of the west coast of Asia Minor). Homer's Iliad and Odyssey were written in a kind of literary Ionic with some loan words from the other dialects. Ionic, therefore, became the primary literary language of ancient Greece until the ascendancy of Athens in the late 5th century. Doric