ABANDONED. Book with brothers who are separated in a different time

[Noah]

I am trying to remember a book I read when I was in Middle School (circa 2006) that involved two brothers that were sucked through some sort of time portal/dimension into a medieval period with magic/etc. I remember only a few details, in particular when one of the main characters was trying to fortify the walls of the city for defense. He and another character (I remember him being a large, strong giant character) found some extremely strong rocks that they could not break that they harvested and used to fortify the walls of the city. There was another point in the book where the main character had to fight a monster in a maze/cave like setting. Again, sorry for the incredible lack of detail. thanks for the help!

[Capn]

Hey Noah,

Are you still looking, or have you found this in the meantime? :) (If you know the title, please share!)

In case you are still looking, there's now a juvenile fiction list for mazes:
https://www.goodreads.com/list/show/1...

[Rainbowheart]

The Brothers Lionheart?

[Kris]

No response, moving to Abandoned folder.

Noah (OP) was last active on the site in July 2019.