Not that I want to claim to be historically accurate (and who can, considering it is only rumor), but the speculation that she was 'good' to her horses gets my imagination stirring!
So, maybe it happened like this...
Our not yet horsebred Russkie is not allowed loose comingling, both for bloodlines and for security, but she is eighteen, devoid of her 'flower' thanks to a (helpful?) servant, and becoming addicted to dick!
The servant didn't realize she'd love it so much but if he refused to service her, and as often as she wanted, he knew his life would be in danger; so he continued to service young Catherine, even though he knew it was only a matter of time before she got pregnant. (Fortunately, he had only gotten involved in the first place after checking her 'monthly' schedule.)
With these brains, this guy should've been czar!
First of all, Catherine was a BIG girl, over six feet, and our faithful servant, try as he might, never remembered bottoming out. Fact was, she had a special bathtub because her hips were so wide, but not from fat! She was 'big boned' (no pun intended, yet).
So, this one night, right after her latest period, he sneaks into her chamber, naked, and begins by probing her with his fist!
Unshaken, Catherine isn't even sure, right away, that is WAS his fist!
Her eyes closed, her mouth purring, her tunnel of love dripping, he was into her, past his wrist, when she popped her eyes open, and only because of the new tingle it gave her, not any pain. That's when she noticed he was experimenting with her, and she loved every minute of it!
"More," she ordered, "more!"
So, (let's give our servant a name, but an easy to spell, Russkie, name) Ivan drills deeper with his forearm, but about two-thirds up each male's forearm, especially if they perform physically, the width gets dramatically larger, and such was the case with Ivan. Still, she had to be taking twelve inches, and still wanted more!
But now it was a question of width, and the next inch never made it. She wanted more!
Now, Ivan had nothing left but his own pole and he chose the best position he could to attain maximum penetration.
With Catherine already primed, he just slid right into her, slowly, all in one slow motion, until his pelvic bone slapped hers, and then he commenced to pound her for all he was worth!
But the deed had been done!
By fisting her, first, it was now like placing a 'c' battery into a 'd' cell receptacle, in today's terms!
Catherine was getting pissed; which means Ivan's life might be in grave danger!
Fortunately for Ivan, he abused her love button for the next hour, she was THAT insatiable, and he promised to 'show' her something, the next day, when they were going for her 'riding' lesson.
Now, the Russians are proud of things, homegrown, but Arabian stallions had established their superiority over a thousand years before, and her stallion, Mohammed, was the best of the lot!
Smooth gallop, quite obedient, and not easily overexerted, were all trademarks of such a fine steed.
As Ivan & Catherine galloped to a secluded stream that Ivan had in mind, he let the horses free to drink and motioned Catherine to watch!
As horses in perfect repose are sometimes wont to do, (and Mohammed didn't disappoint, especially after a gallop) their monstrous appendages tend to dangle!
Catherine's wide eyed fascination confirmed Ivan's wish that she were interested, and then she spoke, "Yes, but how?"
Ivan spread out a blanket on a small rise just above the stream where he had walked the horses on their way to drink.
Catherine was naked in a trice and took her position as Ivan gently grabbed the horses' reins, gently aiming them downstream until he found a treebranch on which he tied HIS horse.
Then, he gently turned Mohammed back toward his rider, and led him, slowly, slowly, just right, until his forelegs were just astride Catherine.
Mohammed immediately got a whiff (animals, remember, use their sense of smell so much more than humans) and lowered his snout to the source.
Now, with all the action Catherine had had, it was going to take a lot more than horse 'face' to get her off, but Mohammed was only confirming what his nose had discovered. His thick, veiny, black phallus was already hanging out of its sheath by twelve or so inches!
Ivan said, "Look Catherine, look down!" and she smiled, lifted her legs up to take hold, better yet, aim his rampant ramrod.
Like only nature can do, the moment, the exact moment his tip lodged, Mohammed bolted slightly!
This wouldn't harm another horse, but could kill a human!
Catherine wasn't your normal human - she took that first five or so inches (she was wet the moment she saw it) and tried to scoot down for more!
Ivan saw this and quickly warned her, "No, don't, WAIT!"
Just as she stopped, Mohammed bolted another eight inches into her!
Now, her eyes popped open, in surprise, but not pain as Mohammed looked to plant the last of his penis: he was getting ready to deliver his seed!
Ivan warned Catherine to scoot back quickly and she did, so that the next bolt didn't enter her any more, but Mohammed was starting to cum!
"Kick him out! Now!" warned Ivan; and as she did, Mohammed's penis exploded its Arabian milk, drenching her from stem to stern!
.... There is more of this story ...