Sanctuary has multiple meanings. A sanctuary is the consecrated area of a church or temple around its tabernacle or altar. An animal sanctuary is a place where animals live and are protected. In modern parlance the term is used to mean a place of safety.
In Europe, Christian churches were sometimes built on land considered as a particularly 'holy spot', perhaps where a miracle or martyrdom had taken place or where a holy person was buried. Examples are St. Peter's Basilica in Rome and St. Albans Cathedral in England, which commemorate the martyrdom of Saint Peter (the first Pope, according to Catholics) and Saint Alban (the first Christian martyr in Britain), respectively. The place, and therefore the church built there, was considered to have been sanctified (made holy) by what happened there. In modern times, the Roman Catholic Church has continued this practice by placing in the altar of each church, when it is consecrated for use, a box (the sepulcrum) containing relics of a saint. The relics box is removed when the church is taken out of use as a church. In the Eastern Orthodox Church, the antimension on the altar serves a similar function. It is a cloth icon of Christ's body taken down from the cross, and typically has the relics of a saint sewn into it. In addition, it is signed by the parish's bishop, and represents his authorization and blessing for the Eucharist to be celebrated on that altar.