Stallions behavior

I honestly it just depends on the pasturing set-up and personality of the horses.

We only have two breeding stallions right now, a donkey jack and a miniature horse (31") and they are seperated because the jack is very aggressive during breeding season. Back three or four years ago though, we had two other stallions (one has since passed from colic and the other was sold) and we had no problem with pasturing them together. When we first introduced them it was with a 5' tall sheep-fenced (so they couldn't take a bite out of eachother) in between them. We let them sort out their differences in there for a week or two, then turned them out togther in a 3 acre pasture. That gaves them enough room to chase eachother around without anyone getting cornered, and we never had a problem with them. They didn't fight, didn't play, really didn't even hang around eachother. However, they were pastured far away from all of our mares and were checked twice a day for the entire time that we had them together (I think about a year).

If possible though, I would advise in not risking it. As someone already said, stallions can and will fight to the death if given even part of a reason to.

Thank you all for your input. I am greatful that you all warned me against having them together. I divided my barn into 2 indoor/outdoor corals with pipe gates and they are both big enough for all 4 minis or just one, but am glad I have them as my little 26" stud wants to eat my baby. Lol The baby keeps getting just close enough to the fence to be out of reach of the other one to tease him. Lol onery little stinker he is!

Have seen some together in winter, they get along good. Some would not, so if you plan on it, I would try across a fence first.

Like everyone else has said there are more factors to it than just the fact of them being stallions. But I have had two very contrasting experiences of it that Ill relate, just to show the contrast.
Most of the horse riding/training I do now is for my uncle who is slowly beginning to build up his heard again after it was decimated by drought in Queensland a few years ago (Queenslanders will know what I’m talking about). He has two stallions, one is the younger brother to most of his brood mares, the other is one he bred from another source; so the second one gets most of the fun not being related to any of the mares. They live on the same place, and just out in the paddock, never in a stall or anything, and on opposite ends of the place. And in between is my old gelding who is in he’s early 20s (is half brother to the older stallion [shouldda been the one kept as a stallion in my opinion]) and for the most part is just an eating machine these days. The two stallions are pretty aggressive, if they get a whiff of a mare they strut about kind of the way you will see 20 something boys do in a nightclub, and act about as obnoxiously too. So any time we have any horses around they get thrown in the middle with my old gelding, who though being a gelding, decides he is “the man” and struts about with his little harem of mares.
On occasion the older of the stallions has jumped the fence and gotten into my geldings paddock, (the whole breed have always made good jumpers, particularly for quarter horses) and my old guy thought it was time to show little brother just who he was about to mess with. Well eventually, my old guy managed to hide cowering in a thicket of mulga when it sunk in that there is just a slight difference between the power and aggression of a stallion compared to a gelding. On another occasion the same Stallion broke the fence again to get at the mares we had there that I was training. So we went and caught him and put him in the yard so the 4 mares, my new colt and my old guy would last the night. The trouble with this though was that down one side of the yards, all 6 to 7 foot split wood railing, forms the edge of the paddock of the other stallion, also a Quarter Horse. That night, even with the railings between them they went at it with the result being a hunk of lip being almost torn clean off the older of the two stallions, the younger one, we think, must have lost the fight because he was pretty sulky and subdued for a week or two. So even with a big solid wooden railing fence between them they went at it, no fence one of them probably would have been killed.
But on the totally opposite end of the spectrum, the Bedouin tribe I lived with in Jordan never geld anything. They have them wandering around the village all day, have them stabled next to each other, have them ridden around beside each other all the time, feed them together, though usually a few meters apart, and I only ever heard of one fight, which unfortunately one of the brothers in my Bedouin family tried to break up and had the whole top row of his teeth kicked out. So Stallions can also be kept together with no trouble at all too.
Having said all that though my advice would be to err on the side of caution, keep them separated.

We have 4 stallions together :) No problem at all, but then we have no mares at our place either.