Freeciv

The comment near this value says: "how much it helps for defenders to be ground units". Some other comments tell us that this value used to have various values in soe former versions. Currently assess_danger() sets this value to either 90 (if there is any potential unit that by a pathfinder's path or by paradropping seems to be able to get to the city) or 5 (if no danger is visible to the "omniscent" dummy). Then:

• assess_defense() that is called from many places multiplies the unit's defense on floor(sqrt(wall_value / 10));
• dai_process_defender_want() multiplies desire for a unit (basically, its squared rating without effects) if it is not a "BadCityDefender" on wall_value, so 1/2 if the city is not threatened and 9 if it is. I can't see any connection to "BadCityDefender" flag since it's already figured out in desire for not calculating firepower, we should just halve the unsquared desire cuz it also doubles the attacker's attack.