Eastern (also called Greek) Orthodox Christianity, which is related but not identical with the Orthodox Church. In many ways, Orthodox Christianity is the ultimate traditional society as is best embodied by its spiritual center, namely Mount Athos in Greece. At the heart of Orthodox Christianity is the conviction that what has been received from previous generations must be passed on intact and unchanged. In particular, the liturgical practices (and most notably the celebration of the Eucharist or mass) are deemed immutable and follow an ancient text written in the fourth century but based on a similar earlier source.
It is possible that certain branches of Orthodox Christianity will embrace a more flexible approach to traditionalism but it is equally certain that the majority (notably the Russian Church but also Mount Athos) will retain a strong traditionalistic approach.