Roman Cavalry saddles

[Ygraine]

I was just reading one of Jack Whyte's terrific works of historical fiction, The Lance Thrower. In the foreward, he stated that the stirruped saddle was generally believed to have been introduced to Western Europe by the Franks. I had previously read in other sources, that the Arab peoples had used the stirruped saddles first, and they came to Europe via trade. Others believe that the Franks may have gotten them from Asians. So, my questions are:

1) Who first used saddles with stirrups?
2) Who introduced them to Europe?
3) Did the Roman Army use them, and if so, when?

Thanks to all who can contribute any insights.