Charles Ellicott Commentary Joshua 22:19

"Howbeit, if the land of your possession be unclean, then pass ye over unto the land of the possession of Jehovah, wherein Jehovah`s tabernacle dwelleth, and take possession among us: but rebel not against Jehovah, nor rebel against us, in building you an altar besides the altar of Jehovah our God." — Joshua 22:19 (ASV)

If the land of your possession be unclean. —This suggests that they might have built the altar in it to sanctify it. But it would hardly be intelligible unless the altar was, as we supposed, on the eastern side.