How did the name Britain come from?

Britain consists of two islands located on the northwest border of Europe-Britain and Ireland. The original inhabitants of Britain were Iberians. They have lived there since 3000 BC, and they brought the Neolithic culture to Britain. These Iberians come from the Iberian Peninsula where Spain and Portugal are located today. They are short and dark-skinned. Later, when history entered the Iron Age, Celts from the mainland began to invade these two islands in northwest Europe-Britain and Ireland. Among these Celtic tribes, bretons has the largest number. These tall, blond Celts gradually conquered and assimilated the Iberians on the island and became the main residents of the island. Celts first lived in the south of Germany today. They were the first people in Europe to learn how to make and use iron and gold ornaments. Before conquering Britain, the Celts conquered today's France, Spain, Portugal, Italy and other regions. One way of saying that the name "Britain" comes from is that mainlanders call people in the British Isles "islanders" and "people by the sea" (that is, "Brittany"), while Romans call it "Britain".