A martyrium, (pl: martyria), (From Latin: martyrium, ancient Greek: μαρτύριον (martyrion, “testimony”)), in Christian usage refers to a structure or building that is built on sites connected with certain events in the life of Jesus Christ and other places held to be sanctified by the sacrifice of the martyrs.
The structure of a martyrium is usually circular or polygonal and is built over the tomb of a Christian martyr. It is essentially a mausoleum or crypt. In some usages martyrium may be used interchangeably with crypt. The form of martyria came from well-established Roman funerary types such as octagons and rotundas and, in early Christian architecture, formed a distinct emphasis on a centralized plan, which was of round, polygonal, or cruciform shape. In buildings, such as Saint Peter's in Rome and the Holy Sepulchre in Jerusalem, the martyrium structure and basilica were combined, which created a new synthesis of significance for religious architecture.