Narrow fixed corridors that are the only legal way for non-scouts to cross into enemy territory during Ramp-Up.
Under Ramp-up Phase rules, egress into enemy territory by anyone other than a scout is only permitted through narrow, kilometer-wide gates, and each corridor stays in the same spot for the whole phase. Baroness Victory points out that the corridor into the Princess Posse's land opens exactly where the enemy is massing.
This is simultaneously the Posse's greatest danger and their best hope. Carl hates that his people can only cross borders through a kilometer-wide gap while stripped of teleports and offensive magic, but Victory frames it the other way: there are only two entry points into their land, and if they can guard both, they survive. Once enemies are through a gate, however, they can move freely, which is why Florin's trenches and traps are concentrated on the approach.
Fixed kilometer-wide corridors on the territorial borders, sited where the armies already stand.
The chokepoints that define the Princess Posse's defensive problem during Ramp-Up.