During these three centuries we have very little outside evidence as to the character of the religion professed by any of the Scandinavian peoples, and our knowledge of the beliefs and practices of northern heathenism is for the most part derived from native sources of a later date. These, while in some respects copious enough, by no means give all the information that could be desired, and on some important points their evidence is either scanty or very unsatisfactory. The deficiencies are to a large extent disguised, at first sight, by the fact that we possess abundant information as to Scandinavian _mythology_. Not only do the poems of the skalds (from the close of the ninth century onwards) abound in mythological allusions, but there also exists a systematic account of the subject in the work of Snorri Sturluson, commonly known as the 'Prose Edda,' written in Iceland about the year 1220. For the facts relating to the actual _religion_, on the other hand, we have to depend on the few pieces of outside evidence, and on fairly numerous, but not always reliable, statements in the biographical and historical prose writings commonly grouped together under the name of 'Sagas.' These works, based on oral tradition of a very full and often very accurate nature, were written in Iceland during the twelfth and thirteenth centuries, and most of them are separated by more than a century and a half from the period of time to which they relate. As the authors were in every case Christians, and many of them were ecclesiastics, it is obvious that the late evidence thus afforded us is not to be absolutely relied upon. On the other hand, the tenacity of Icelandic tradition, the continuous interest in the poetic mythology, and the absence of any fanatical hatred of the old heathenism, make it possible to accept, with due reservations, many of the statements made in these writings. It is unfortunate, however, that Iceland alone of all the Scandinavian countries developed a literature of this kind. The result is that the information thus preserved relates for the most part only to Iceland itself and its mother-country, Norway. The heathen period in Denmark was so remote, and Sweden itself so slightly connected with Iceland, that comparatively little is recorded of either, although Sweden was still heathen when Icelandic literature began. This is the more to be regretted, as a fuller knowledge of the precise form which the old religion had in Denmark and Sweden would in all probability solve some problems which are now obscure.