Thedog

As king, he would be direct lord of the Crownlands. That region doesn’t fall within any of his primary vassals’ domains. Accordingly lesser houses from the Crownlands would be his direct vassal, and likely the crown would also hold land within that region directly. So he could certainly recruit men from that land. Additionally he could recruit directly from King’s Landing. Targaryens had no problem finding men to be Dragonkeepers, and presumably had guards in addition to the watch.

A Queen he prestige through her husband. Tywin having men at court would seem to indicate that he thought that there would be situations where he thought Cersei might need swords who are not beholden to Robert (at least not any more beholden than any random commoner in Westeros). I guess that knowing Cersei her getting into a situation needing men did seem like a good precaution. nevertheless, i still Don’t get why Robert would let a force of men not loyal to him be permanently lodged under his roof. Obviously there is precedent for a Queen having a sworn shield (in this case the Hound). But a force of armed men? That seems to undercut his power.

So at the start of the Game of Thrones (ie during peacetime), there are random Lannister men-at-arms just hanging around King’s Landing. Why? Lord Tywin is not present, and they are his men. Jamie is a Kingsguard, so he shouldn’t have a retinue of guards. They are not there for Tyrion since apparently only keeps only two retainers. I know you might say Cersei, but that doesn’t make a lot of sense. Daughters of great lords are always marrying into other families and they then use the guards of the new family. There are no Tully men hanging around Winterfell or the Vale, with the Tully daughters (well the Blackfish goes to the Vale, but it appears that he is not with a contingent of men). They apparently expect the loyalty of their husbands men. So why are there so many Lannister soldiers hanging around King Robert? It seem that Robert would and should object to this. He should have Baratheon men in droves, since he now controls the Crownlands directly, but it seems like all he has are the City Watch.