what with all the reigning queens littering the landscape

One of the things I find the most fascinating about sixteenth-century Europe is the way that, for a whole confluence of reasons, the landscape was littered with reigning queens and female Heirs Possible and the occasional woman (Diane de Poitiers) who may not have had a crown but you couldn't tell it to look at her. I don't know of any other time period when there were so many of them at once.