Barricades should act like a zone of control and slow units to one move each. In this game, I've noticed that Babylon knights were passing through the zone of control under fire but not without any movement penalty.

Barricade.SAV (http://ourworld.cs.com/Gebaupointy/Barricade.SAV)

Edit: This is the Beta Patch 1.12 version.

IIRC Barricades only slow movement for units moving ONTO the Barricade tile. Pretty sucky really.

The Fortress is what gives the (Civ3 style) ZOC, which is purely a chance of 'free shots' at passers-by.