Tavis over at The Mule Abides posted a fascinating entry about how, in medieval Krakow, various guilds were charged with maintaining the defense of different towers and gates along the city walls.
This clicked with something that's been sitting in the back of my brain for a while. One of the Minifigs World of Greyhawk miniatures packs was entitled "WOG08 Infantry of the Guilds (6) spears, crossbows - Greyhawk" (I don't have a pic available, but will update both that page and this post if I ever find one). For years I wondered what the heck "infantry of the guilds" might have been. Were they engaged in combat in the very streets of the city? Now it all falls into place.
In time of war, the various guilds of the City of Greyhawk, much like those of the city of Krakow, would be called upon to man the defenses, doubtless in a similar fashion, with each guild being assigned a particular tower, section of wall, and/or gate. This would function as a sort of auxiliary, allowing the regular soldiery to take the field or, during times of siege, run the defenses of the city, with the guild troops as backup.
Among the mysteries of the universe, this certainly is one of the most minor. But I'm glad to have it solved, at least to my satisfaction. Thanks, Tavis!