Formerly, barring some unforeseen circumstances it was not possible to march legions past raised fortifications of ANY kind, including those on your own home soil or part of your wider sphere of village influence.
This has now changed, with the following specifics:
City fortifications will NOT block passage either direction by legions sharing the same city association as the forts. Thakrian troops therefore can pass in and out of Thakrian forts raised or not.
Wildland, town and village (wider SOI forts) will NOT block legion passage of troops loyal to the city whose flag is in the location with the fortifications. Therefore if Mercinae has flagged the marshes, their troops will be able to pass any forts there with the Mercinaen flag.
Talk to me if any of this is unclear, and as always: report any issues with forts, legion engagement or warfare of any kind immediately.
Elmaethor, god of the stars
Written and shown unedited exactly as rendered by text based game bulletin board on Avalon Online RPG and by my hand on the 29th of Springflower, in the year 1382.