Beowulf is the oldest long poem in English. It was written in what we now consider Old English (Anglo-Saxon). To the modern English speaker, Old English will sound like a different language and this is on account of its old Germanic roots. Some scholars say that the poem was written perhaps more than 1200 years ago in the 8th century. Some say it was written later in the 10th century. The author (unknown) is believed to have been from Mercia, what is now known as the English Midlands. This is the middle belt of England. However, the earliest version that we have is a 10th century manuscript originating from the West Saxon Kingdom (south of the Midlands). In 1731, a fire destroyed part of the poem and this was never recovered.
The poem was written in Old English but it deals with Germanic ancestors, the Danes and the Geats. These Danes were from the Denmark island called Zealand and the Geats were from southern Sweden. Although the poem was probably written sometime between the 8th and 10th centuries, it deals with a time probably around the mid 5th century. The poem does mention a known historical fact and this was the invasion of the Franks by Hygelac, king of the Geats in 520, a time when Beowulf would have been a young man. Beowulf is believed to have been a Geat himself. Even though the poem's subject matter would have been 3 to 5 centuries old at the time, the reading audience would have been familiar with Beowulf's story. And some readers/listeners likely believed that they descended from Geats themselves.
Most scholars agree that the Beowulf poet was a Christian. But scholars disagree as to what degree the poem illustrates Christian beliefs and to what extent the poem illustrates a more ancient, pagan belief system. It seems that both influences played a role in the poem's construction.