Though roof tiles similar to those of Taga-jo Castle were found in the Koriyama Ruins at the place that was later called Koriyama-haiji Temple, research had been untouched for a long time.
郡山遺跡からは、後に郡山廃寺と名づけられた場所から、多賀城のものと似た瓦が見つかっていたが、長く調査の手がつけられなかった。