Antimins

The antimins (from the Greek Ἀντιμήνσιον, Antimension: "instead of the table"), is one of the most important furnishings of the altar in many Eastern Christian liturgical traditions. It is a rectangular piece of cloth of either linen or silk, typically decorated with representations of the Descent of Christ from the Cross, the Four Evangelists, and inscriptions related to the Passion. A small relic of a martyr is sewn into it. In the Latin Church of the Catholic Church, the altar stone serves a similar function.

Syriac practice
A wooden tablet, the ţablîtho, is the liturgical equivalent of the antimins in the churches of Syriac tradition.