Book 13, Ch. 9: Dawn Comes

I am told to find Aragorn and Théoden on the field outside the gates but when I exit the Helm's Deep gates the quest arrow on my map says the location is 30,443 m away and when I look at the map I do not see any indicator as to where it is. I also do not have the option to use Mithril to travel to the location. From the quest arrow they do not appear to be anywhere within Rohan. I am very confused.

How/where do I find Aragorn and Théoden to complete this part of the epic?