After the end of the Mycenaean period, the art of writing was lost in Greece: by the ninth century probably no Greeks understood the Bronze Age Linear B writing system. From the ninth century BC, however, objects inscribed with Phoenician writing began to be brought into the Greek world, and it was from this Phoenician script that the Greek alphabet developed in the eighth century BC. By the middle of the eighth century BC, pottery inscribed in Greek begins to occur in the archaeological record.
The earliest known inscriptions in Greek tend to identify or explain the object on which they are inscribed. Possibly the earliest known Greek inscription is found on a jug from the first half of the eighth century BC, discovered in Osteria dell’Osa in Latium. Most early inscriptions were written in verse, though some from Ionia were in prose, influenced by the prose traditions of Ionia’s eastern neighbours. From the beginning of the seventh century, curses and dedications began to be inscribed on objects, and by the sixth century, surviving inscriptions include public records such as law codes, lists of officials, and records of treaties.
Source: Wikipedia