question regarding sentinels

hello people,
ive been trying to think of a scene in lotr
two hobbits are in a boat on a river , it must be frodo and sam, post lorien maybe,
they are floating down the river and they pass some ancient giant stone statues that are old watching sentinels or something.
does anybody remember what they are and if they have a name?

ive been making a painting that i realised was inspired by a vague memory of these sentinels so i thought i should try to figure it out...

ok if anybody knows this stuff i figured i could find them here!
thanks

-sonja