The 300-year period in Greece beginning around 1100 BC refers to the era known as the "Geometric period" which is part of the wider context of Greek history often marked by the transition from the Mycenaean civilization to the development of the city-states, leading eventually to the Archaic period.
This period, roughly from 1100 BC to 800 BC, is characterized by a decline in population and trade, following the collapse of the Mycenaean palatial societies. It was during this time that the foundations for later developments in Greek culture began to take shape, including the emergence of small settlements, the revival of pottery with geometric decorations, and the beginnings of the use of the Greek alphabet.
If you meant a different historical period or context, please clarify, and I'll be glad to provide more information!