A prayer rope (chotki in Russian, komboskini in Greek) is a loop made up of knots, usually made of wool, that is used to keep track of the number of prayers which have been said. It is usually used with the Jesus Prayer: "Lord Jesus Christ, Son of God, have mercy on me, a sinner." Historically it typically had 100 knots, although prayer ropes with 50 or 33 knots can also be found in use today. There is typically a knotted cross at one end, and a few beads at certain intervals between the knots.
Its invention is attributed to Saint Pachomius in the fourth century as an aid for illiterate monks to accomplish a consistent number of prayers and prostrations. Monks were often expected to carry a prayer rope with them, to remind them to pray constantly in accordance with Saint Paul's injunction in I Thessalonians 5:17, "Pray without ceasing."
In some Russian Orthodox service books, certain services can be replaced at need by praying the Jesus Prayer a specified number of times, anywhere from 300 to 1,500 times depending on the service being replaced. In this way prayers can still be said even if the service books are unavailable for some reason. The use of a prayer rope is a very practical tool in such cases, simply for keeping count of the prayers said.