In 839 Swedish vikings reached Miklagaard (Istanbul), they did not manage to sack the city.
Vikings stayed for the winter 839-40 in Ireland after a series of great victories against the Irish. They mad a camp at Lough Neagh which they occupied for 3 years.
Vikings also defeated the Picts in their own kingdom. In a major battle in 839, the Vikings killed the king of Fortiu and the king of the Scots Dál Riata
Frisia was attacked by a viking fleet