Open syllable lengthening affected the stressed syllables of all Germanic languages in their history to some degree. Curiously, it seems to have affected the languages around a similar time, between the 12th and the 16th centuries, during the late Middle Ages. The languages differ mainly as to the specific vowels that were lengthened the specific environment but also in the result of the lengthening. There is substantial variation, and in many languages, the process has been obscured by paradigmatic levelling. Sometimes, the newly-lengthened vowels merged with existing long vowels, but in other languages, they remained distinct because the older long vowels underwent changes of their own such as in Icelandic and, to a lesser degree, the continental Scandinavian languages.