A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
A player, 8 September 2013
The Tower of Vigilance reads, "Engage, (Bow): If you have any Personalities at this battlefield..."
Does "this battlefield" refer to the current battlefield, or to battlefields associated with the province to which the Tower attached when it entered play?
In other words, if the Tower is attached to Province B, but we are conducting a battle at a battlefield associated with Province B, may I use the Tower of Vigilance's Engage ability at the Province B battlefield (assuming that I have a Personality at battlefield B)?
A player, 8 September 2013
You can only use abilities from Fortifications during battles at their own province. Therefore, you cannot use Tower of Vigilance in battles other than the one at the province where the Tower of Vigilance is attached.