What kind of levels do you give a city guard patrol? 1st level Warriors? 5th level Fighters?
In my campaign, the PC's are at a rural castle, along on a major river, facing the Yatil Mountains.
With the help of the PC's (3rd level Warrior thru 7th level Monk and Fighter themselves), the local troops have just defeated a small enemy commando force of werewolves (with PC class levels, typically about 2, as high as 9th for the leader) and orcs (straight up normal orcs, except for those who are gifted with lycanthropy.
The tower guards were 1st level Warriors, with 2nd-3rd level Warrior sergeants (one became a PC for a new player), a 5th level Fighter captain (IIRC), a few 2nd level PC classed characters and a Adept, and a 3-4 level Aristocrat lord. Since it's a frontier area, there was also a large militia in the various hamlets of the manor. For this, I followed the 3e DMG on levels and classes, ignoring PC classes -- so in the hamlet where the first battle took place, the leaders were a 4th level Expert (stat'd to be fisherman who can fight) and 5th level Commoner (stat'd to be a farmer), a few of the troops were Experts with light crossbows and daggers, and most of the troops were Commoner 1 with a spear and two javelins (that is, equipped as Irish kerns). The hamlet militia pretty much destroyed an orc force of about equal size, because they had early warning and were able to both pepper the orcs with missile weapons and set against a charge. Once the werewolves entered the fray, they ran for it, and only the timely arrival of PC's on horseback let most of them escape.
BTW, I highly recommend Medieval II Total War, to learn about medieval troops and because it's an amazingly good game. Equal to, if not greater than Temple of Elemental Evil -- and that's Greyhawk 3e, what could be better (working at all on Windows XP, like it claims it does, would be nice for TOEE).