The Samaritans are, by the measure of continuous practice, one of the oldest living religions on earth, and one of the smallest, about eight hundred people in total.
The disagreement with Judaism. Samaritans and Jews share the Torah and diverge on almost nothing so sharply as the place of worship. Where the Jewish scriptures make Jerusalem and Mount Zion the chosen site, the Samaritan Torah makes Mount Gerizim the place God chose for the altar. Each tradition holds the other's central sanctuary illegitimate. A Samaritan temple stood on Gerizim until the Hasmonean ruler John Hyrcanus destroyed it late in the second century BCE, and excavation of the summit has uncovered the sacred precinct and town of that era.
The living sacrifice. The Samaritans still perform the paschal sacrifice described in Exodus: on the eve of Passover the whole community assembles on the mountain, sheep are slaughtered on open-air altars, the blood marks the foreheads of the participants, and the meat is roasted overnight and eaten. This is the only place on earth where the biblical Passover sacrifice is still carried out, unbroken. It is a rite, not a re-enactment, though the community admits observers.
Survival by neutrality. The community nearly vanished, falling to a few hundred by the early twentieth century, and has slowly grown. Half now live in the West Bank village of Kiryat Luza, built in the 1980s after they left Nablus, and half in Holon near Tel Aviv. The Samaritans hold both Israeli and Palestinian documents and keep a studied neutrality between the two peoples around them, part of how so tiny a group has endured in so contested a place.