Whole books have been written on this subject so this is just a brief description. Runes, as you can see in the pictures above, were a simple form of writing. Note that curves and circles play no part in runic scripts. Each rune is a variation on a vertical line. The reason for this is that they were intended to be inscribed mainly on wood - particularly on bark - and on stone. In the case of wood it was therefore possible to mostly carve along the grain, making the whole task so much easier. Ancient cuneiform script was also, by and large, based on straight lines although the characters were often much more elaborate than runic scripts. We might see runes as being a continuation of an age-old tradition of devising forms of writing designed to best fit the writing materials available. Cuneiform, for example, was used to carve on clay tablets with a stylus.
As with so many things, runes have become the stuff of fantasy and mythology and so “rune” has become associated with any old pictorial alphabet real and imagined!
In the western Roman Empire Latin gradually supplanted Greek and local Italian dialects. This was not a cultural imposition: rather that the various peoples that traded with Rome adopted it out of economic necessity. There is an obvious parallel in the modern world where vast swathes of the world’s population are learning English - or perhaps, more accurately, American! The eastern lands of the Roman Empire did not adopt Latin. It is important to remember this because it explains why the Gospels were written not in Latin as most people suppose but in Greek. After the division of the Empire, the Eastern Empire - later the Byzantine Empire - retained Greek as the language of administration and government.
Many of the Germanic tribes defied incorporation into the Empire for centuries, of course, and eventually sacked Rome itself. As Rome’s foes they had no need to adopt Latin and they retained their Germanic languages. The Scandinavian races themselves were culturally and linguistically Germanic and, of course, were not at all involved with Rome. The Germanic people seemed to have started using runic script for communication from about AD150. It is believed that the Goths may have become familiar with writing through trade with Greek lands as long ago as the sixth century BC and, significantly, some of them formed the province that is still called Gothland in what is now Sweden.
The Christianisation of Europe led to runes being steadily supplanted by Latin. Christianity, however, did not fully eradicate pagan beliefs in Scandinavia until as late as the twelfth century. The Manx crosses show us that even when Christianity was adopted, it did not immediately supplant the pagan gods: rather the Viking people assimilated Christianity and initially saw no contradiction in juxtaposing Christ and Odin in their belief system. Vikings did not worship their gods in the way monotheistic religions do; rather they propitiated and reached an accommodation with them. Perhaps the biggest myth in the history of Christianity in Britain and elsewhere is the concept that people became “converted” and promptly dropped all pagan beliefs and superstitions. Remember that the next time you see a Green Man grinning at you in a church and some fool tries to convince you that is has a Christian symbolism!
Given all of this, the Vikings did not, of course, adopt Latin at all. Unsurprisingly then, they also hung onto runic script for much longer than in the rest of Europe. Interestingly, runes are also confined to certain areas of England. That seems to be connected to which of the so-called “Saxon” tribes colonised any given region. The Saxons themselves seem not to have used runes. The Jutes and the Angles did and so runes are most common in areas that they settled - East Kent and the North of England respectively. Kent, of course, was Christianised quite quickly since this was the stronghold of St Augustine’s mission from Rome. Other parts of the country hung onto runes much longer and, as we have seen, the Isle of Man was particularly isolated from Rome’s brand of Christianity and the Latin that was its principal language.
Being Germanic peoples, it seems that Vikings and “Anglo-Saxons” were able in part to communicate with each other, so runes would have been very useful. There were, however, different varieties of runic alphabet although all of them share many of the “letters”. That’s not really surprising because this was a “folk” form of communication, not a scholarly one. The ones used in the Isle of Man originated in Norway and they are, therefore later than the Gothic runes which arrived in Kent via the Jutes in the 5th or 6th centuries and those found in Northumbria and Cumbria introduced by the Angles in the 7th century. You can see a fine example of Cumbrian runes on the Norman font at Bridekirk.