Walker behavior under triumphal arches can be weird, in at least 3 ways.
Walkers behave as would be expected under a triumphal arch with its road running NE-SW. All walkers treat the road through the arch as a road. (Houses can exist near the road through the arch without other roads nearby.)
Weirdness 1: Walker behavior is affected by triumphal arch orientation. A triumphal arch built on bare ground with its road running SE-NW has a different effect on walkers than is described in the previous paragraph. Destination walkers (including random walkers heading to their "walk target" or back to their building) will use the road through the arch, but random walkers who are just roaming around are blocked. (Houses cannot exist near the road through the arch without other roads nearby.)
Weirdness 2: Walker behavior is affected by the roads that a triumphal arch with its road running SE-NW is built on. A triumphal arch with its road running SE-NW built on top of such a road (and no other roads) behaves differently. The road through the arch is treated by walkers (and houses) as a normal road (like a triumphal arch with its road running NE-SW), but that's not all (see the next paragraph). A triumphal arch with its road running SE-NW built on the center of a road X has the same effect on walkers (described in the previous paragraph) as if it had been built on bare ground. I didn't try building triumphal arches on any other road configurations.
Weirdness 3: The columns of the arch may sometimes act like roads. A triumphal arch with its road running SE-NW built on top of such a road (and no other roads) allows all destination walkers (including random walkers heading to their "walk target" or back to their building) to use the columns of the arch (the middle of the NE and SW sides) as roads (but houses cannot exist near those columns without other roads (such as the road through the arch) nearby). In effect, such an arch behaves as if it had been built on bare ground, the weird roads under it rotated through a right angle, and another normal road added through the arch.
Historical notes: This explains why some players had problems with triumphal arches while others didn't. The first mention I found of triumphal arch problems was reply #5 oftriumphant arch. I mentioned some details in reply #4 of Triumphal Arch Warning, but I didn't figure it out back then since I knew much less about random walker behavior.
Walkers behave as would be expected under a triumphal arch with its road running NE-SW. All walkers treat the road through the arch as a road. (Houses can exist near the road through the arch without other roads nearby.)
Weirdness 1: Walker behavior is affected by triumphal arch orientation. A triumphal arch built on bare ground with its road running SE-NW has a different effect on walkers than is described in the previous paragraph. Destination walkers (including random walkers heading to their "walk target" or back to their building) will use the road through the arch, but random walkers who are just roaming around are blocked. (Houses cannot exist near the road through the arch without other roads nearby.)
Weirdness 2: Walker behavior is affected by the roads that a triumphal arch with its road running SE-NW is built on. A triumphal arch with its road running SE-NW built on top of such a road (and no other roads) behaves differently. The road through the arch is treated by walkers (and houses) as a normal road (like a triumphal arch with its road running NE-SW), but that's not all (see the next paragraph). A triumphal arch with its road running SE-NW built on the center of a road X has the same effect on walkers (described in the previous paragraph) as if it had been built on bare ground. I didn't try building triumphal arches on any other road configurations.
Weirdness 3: The columns of the arch may sometimes act like roads. A triumphal arch with its road running SE-NW built on top of such a road (and no other roads) allows all destination walkers (including random walkers heading to their "walk target" or back to their building) to use the columns of the arch (the middle of the NE and SW sides) as roads (but houses cannot exist near those columns without other roads (such as the road through the arch) nearby). In effect, such an arch behaves as if it had been built on bare ground, the weird roads under it rotated through a right angle, and another normal road added through the arch.
Historical notes: This explains why some players had problems with triumphal arches while others didn't. The first mention I found of triumphal arch problems was reply #5 of