Er, hatetobeapedanticfanboi, but...
There is a road north-south through Ithilien, and also a road east-west from Minas Morgul to Osgiliath. Where they cross was marked by the headless statue of the king. Frodo and Sam couldn't use the north-south road because of the large number of troops moving on it, including those moving up from the south to attack Minas Tirith.
"BOOK NOTE: In the film, Jackson has split the host of Mordor into three groups (the fleet, the Haradrim and the Orcs) each of which moves and arrives as a single unit. As discussed above, this is insufficient to resolve the overwhelming logistics problems of such large armies. However, the books largely resolve this issue."
Sigh. Pedanticfanboimode wasted.
"Naval supply, by riverboat or by ship, is far more efficient than overland supply (moving supplies by water is roughly twenty times more efficient than moving the same supplies by land in the pre-modern era)."
I want the reference for that.
From part II:
"As Clausewitz says (drink!), “Everything in war is very simple, but the simplest thing is hard.”"
Yeah. A Clausewitz drinking game.
[Edit] "Book Note: In the books, Denethor is nowhere near this stupid (this will be a theme)."
I'm glad somebody else saw this. Jackson really screwed up the plot arcs of the humans in the movies.