Mani sent disciples to Egypt, and he traveled as far west as the border of the Roman Empire
to strongholds of Mithra worship, where he tried to associate himself with Mithraism.
<The Early Years of Sassanid Empire and Religious Turmoil in Persia
http://www.iranchamber.com/history/articles/sassanids_religious_turmoil.php>
I'd like to know if "
to strongholds of Mithra worship" is an adjective phrase modifying "the border of the Roman Empire."
Thank you in advance for your help.