Historians today are not sure of their origin, some say Denmark, some say by the coasts of the Black sea and others says northern Italy.
It is however almost certain that they were invented sometime around 0 A.D. They were used all throughout the germanistic regions of that time, and spread from Denmark to both Norway, Sweden and England.
There was two distinct sets of runes: 'Older' which had 24 caracters and 'younger' which had 16. The younger replaced the older at around the eight century.
Sometime during the seventies archaeologists discovered Denmarks oldest letter 62 runes engraved on a human skull! This letter is from ~800 A.D.
When you are reading runes you cannot be sure which way you have to read, as the vikings enscribed them both from the left to the right, and in the reverse direction right to the left. Moreover they sometimes wrote them in a vertical manner where the direction again could be in both directions: up to down, and from down to up.
More facts to follow!