The origin of the Danes is unsettled, but several ancient historical documents and texts refer to them and archaeology has revealed and continues to reveal insights into their culture, beliefs, organization and way of life.
The Danes are first mentioned in the 6th century in Jordanes' Getica (551 AD), by Procopius, and by Gregory of Tours. They spoke Old Norse (dǫnsk tunga), which was shared by the Danes, the people in Norway and Sweden and later Iceland. In his description of Scandza, Jordanes says that the Dani were of the same stock as the Suetidi ("Swedes") and expelled the Heruli and took their lands.
The Old English poems Widsith and Beowulf, as well as works by later Scandinavian writers (notably by Saxo Grammaticus (c. 1200)), also provide some of the original written references to the Danes. According to the 12th century author Sven Aggesen, the mythical King Dan gave name to the Danes.
The Danes spoke Proto-Norse which gradually evolved into the Old Norse language by the end of the Viking Age. Like previous and contemporary people of Scandinavia, the Danes used runes for writing, but did not write much apparently, as they have left no literary legacy except for occasional rune stones and carvings in wood and various items like weapons, utensils and jewellery.
As previous and contemporary peoples of Scandinavia, the tribal Danes were practitioners of the Norse religion. Around 500 AD, many of the Gods of the Norse pantheon had lost their previous significance, except a few such as Thor, Odin and Frey who were increasingly worshipped. During the 10th century of the late Viking Age, the Danes officially adopted Christianity, as evidenced by several rune stones, documents and church buildings. The new Christian influences also show in their art, jewellery and burial practices of the late Viking Age, but the transition was not rapid and definitive and older customs from the Norse religion, remained to be practised to various degrees.
Some sources, such as the Beowulf, point to a very early Arianism in Denmark, but it has been a matter of intense academic debate for many years whether these sources reflect later adjustments or an actual early Germanic Christianity among the Danes in the Iron Age. There are several archaeological artefacts in and from Denmark however, made as early as the 500s, depicting Daniel among the lions, so the Danes must have had some knowledge of and influence from Arian cultures.