Great Yarmouth where it stands now was not there. There were the three flowing rivers named The Bure, the Yare andT the Waveney.
Water of all these 3 rivers mixed together to make an estuary which fall in to ocean. Conjoined rivers known collectively as the Yare. Great Yarmouth is located at the mouth of this Yare.
At the begging of 5th centaury AD, a sandbank appeared at this estuary and got attraction by fishermen. These fishermen started to settle there as this sandbank started to grow.
Over the time, this sandbank became an island and this island became peninsula and connected to main land.
Herring and cod fish were caught by the fishermen and they earned lot of revenue. Due to high earnings, more and more fishermen started to settle there and this town became trade center. .