The crawlers' trench network, all connected by tunnels that can be collapsed on demand.
Both sides in the southern sector have fallback trenches, but the crawlers' are better made. Theirs are all connected with tunnels that can be collapsed on demand, unlike the Enemy Trench System's three unconnected lines, which force any retreating enemy to pop up and cross open land. Tran pointedly notes the enemy's forward trench "isn't anything like ours" — just a straight line with a few bunks.
The positions are under constant fire. The smaller, mobile trebuchets of the Artillery Batteries have less range than the big ones but are still deadly, and they are what has been hitting the crawler trenches, while the big trebuchets pound the base itself. The bombardment is deliberately unceasing, designed to exhaust the crawlers' mages, and during the briefing a rock smashes just above the command position with the sound of a car crash.
An interlinked trench network backed by collapsible tunnels, under continuous trebuchet fire.
The crawlers' defensive works and the jumping-off point for the southern assault.