11. Vikings founded Dublin
Dublin was established by the Vikings themselves, though the way they went about it was pretty brutal. The Vikings created settlements in Iceland, Greenland, Normandy and Newfoundland, Canada, and raided nearby neighbors like Great Britain along the way. Because they were making their way through the area a lot, they started setting up posts.
They invaded Ireland in the early 9th century where they established a kingdom called Dyflin, which later became modern-day Dublin. It was a major trading post and traded anything from precious metals, fabrics, weaponry, and horses. Dyflin was also a stronghold in Ireland, and the Vikings ruled Dublin for 300 years and meld with the Celtic people.