What source are you using.
I recall those from looking up monarchies a few years ago.
Here is the foremost authority of Monarchs and their families in Europe. http://www.almanachdegotha.org/id12.html
Did you mean to say oldest in Europe as the post title? Or most prominent? Britain is certainly the most well known by far, though not the oldest. Perhaps it's one of the oldest still existing in Europe, but not globally.
(post is archived)