What was their religions?

Vikings are well known for all being pagans, with the hatred of the Christian Church, but this if very misleading. Even though almost the entire population of Scandinavia was pagan at the beginning of the Viking Age, the Vikings had many gods, and they then later had no problem to accept the Christian god alongside their own god. The Vikings came into contact with Christianity through their raids, and when they settled in lands with a Christian population, they adopted Christianity quite quickly. Pagans buried their dead with grave goods, but Christians normally didn't, and this makes it relatively easy to spot the change in religion. As part of the process of conversion the Christians took over traditional pagan sites. There is little contemporary evidence, and although there are occasional references to paganism in the Viking sagas (mostly composed in Iceland in the 13th century) we have to remember that these were written down 200 years after the conversion to Christianity. We know that chieftains also had some sort of role as priests, and that pagan worship involved the sacrifice of horses, but not much more. We know rather more about the stories associated with the pagan gods. Besides occasional references in early poems, these stories survived after conversion because it was possible to regard them simply as myths, rather than as the expression of religious beliefs. The main sources of evidence are the Eddas, wonderful literary works which represent the old pagan beliefs as folk tales.