The reason why no forts are functional is probably because there ain't many soldiers in Cyrodiil during OB gameplay. From conversations, we know that many of these forts had been used few years/decades/centuries ago rather then a millenium.

However, the rise of rebellions in provinces (caused by instability in the empire created by Emperor's death) resulted in Ocato sending armies to the provinces leaving cities to protect themeselves and legionaries to patrol the roads to ensure that at least some level of road safety exists. Sending soldiers to the forst would just decrease the defense of IC and roads and give too little in return.

Praise JHUNAL!

Word Merchant... is that the proper mode of address? Should I simply call you "Sir?" I cannot but praise your continuing, tireless efforts to operate in a truly scholarly fashion in an environment increasingly hostile to anything but moral condemnation of the creators of the world we study, as opposed to the enrichment of said world through study and synthesis. You are one who, in response to the gaps in the work of others, responds not with an accusation of "laziness", but rather a display of his own industry. And you do so with a degree of skill that garners respect, unlike my own crotchety approach.

My skills are unequal to the task I have set before me: to thank you for these efforts. I hope I have at least conveyed my feelings.

Well you could EASILY make a few forts with Legion in them, though it wont be as unique as you would expect, unless you wanted to add some captains or something and add you own voice, but i have made 2 forts with legions in them and i erased it becasue it isnt near as fascinating as it sounds unless you make it unique, the guards just slept, ate, talked, patroled the road, returned, ate, talked, slept, repeat, though the roads were safer i do mind you, but i like to kill a few bandits every now and then... kill stealers

I thought that it was explained (At least in TES: IV) that the forts were from the Akaviri invasion of Cyrodiil. (Sorry if this was said already.)

When i did the quest for the countess of Bruma i remember her saying the forts are all about 500 years old and were used in a war against invaders from Akavir an island far off the coast of Morrowind. They were used by both armies and were abandoned quickly after the Akaviri were defeated and had to retreat back across Morrowind.

Isn't that what I basically said in the post just above yours?

Yeah, sorry honestly i only read the first page before deciding to answer the question...