In Eastern Orthodox and Byzantine Catholic churches, an entrance is a procession during which the clergy enter into the sanctuary through the Holy Doors. The origin of these entrances goes back to the early church, when the liturgical books and sacred vessels were kept in special storage rooms for safe keeping and the procession was necessary to bring these objects into the church when needed. Over the centuries, these processions have grown more elaborate, and nowadays are accompanied by incense, candles and liturgical fans. In the liturgical theology of the Orthodox Church, the angels are believed to enter with the clergy into the sanctuary, as evidenced by the prayers which accompany the various entrances.