Plot or Characters - Which comes first?

That's the eternal question for new authors: Must I know the plot before I people it?
Or should I nail down the characters first?

Some writers say it's only possible to develop characters if you already know the story they're about to enliven. After all, without knowing the action, how can you imagine the players who will navigate through it? On the other hand, isn't it better to have strong characters in place who will take the outline of a plot by the scruff of the neck and steer it in directions that you, as author, might not be contemplating? A healthy input, surely?

In writing The Housemaid's Daughter, I combined the two approaches. I didn't create the plot in its entirety before I started writing, because I wanted my characters to influence me, and thereby affect the outcome of the book. And perhaps I hadn't even identified the full cast anyway...

To instil some order into all of this uncertainty, I drew a mind map which showed the action as far as I had envisaged it, plus a tentative cast list. And then I began to write. Luckily, after a few false starts, my tandem approach began to pay off: the characters started to assume real personalities and, through their machinations, the nascent plot became richer and more interesting.

And when I look back at that early, plot-driven mind map?
Some elements of the finished book are totally different from what I imagined, some characters never ever saw a page of action (oops!), and other characters appeared from nowhere to drive the action forward. The mind map was invaluable in giving me enough of a plot to head me in the right direction, but not too rigid a prescription to stifle creativity.
So... Plot vs Character? I think you need both, in sometimes awkward tandem...
What's that familiar Frank Sinatra song?
Love and marriage, love and marriage
Go together like a horse and carriage?