The medieval runes, or the futhork, was a Scandinavian runic alphabet that evolved from the Younger Futhark after the introduction of stung (or dotted) runes at the end of the Viking Age. These stung runes were regular runes with the addition of either a dot diacritic or bar diacritic to indicate that the rune stood for one of its secondary sounds (so an i rune could become an e rune or a j rune when stung). The medieval futhork was fully formed in the early 13th century. Due to the expansion of its character inventory, it was essentially possible to have each character in an inscription correspond to only one phoneme, something which was virtually impossible in Younger Futhark with its small inventory of 16 runes.