north of Osgiliath, which is way out of the way and well-defended (at the
moment), but no reason they couldn't cross the Anduin in boats anywhere except
in the rapids.
Now that you bring it up, though, what about Cair Andros? How does one
get there? specifically, how did the troops that Aragorn sent to retake it get
there, since they wouldn't have any boats with them (not having planned to do
this)? Surely the Anduin isn't
fordable?
sic hobbitur ad astra.
(Entire text of a postcard received by JRRT in 1937, according to Letter #17)