In this excerpt from "the lady of shalott" by alfred, lord tennyson, which synecdoche denotes confinement?
willows whiten, aspens shiver.

the sunbeam showers break and quiver

in the stream that runneth ever

by the island in the river

flowing down to camelot.

four gray walls, and four gray towers

overlook a space of flowers,

and the silent isle imbowers

the lady of shalott.

underneath the bearded barley,

the reaper, reaping late and early,

hears her ever chanting cheerly,

like an angel, singing clearly,

o'er the stream of camelot.

piling the sheaves in furrows airy,

beneath the moon, the reaper weary

listening whispers, ' 'tis the fairy,

lady of shalott.'