GR translation: loops

[Mike Jing]

V3.25-27, P4.1-3   they go in under archways, secret entrances of rotted
concrete that only looked like loops of an underpass . . .

V181.9-12, P183.9-12   Leftward, far away, the ancient aqueduct loops
crumbling, dry yellow, out along the Cap, the houses and villas there baked
to warm rusts, gentle corrosions all through Earth’s colors, pale raw to
deeply burnished.

What exactly are these "loops" referring to in these two cases?