Perched on top of the White Cliffs of Dover with a 360 degree panorama of the English Channel and surrounding countryside lies St. Mary in Castro. The church sits within the English Heritage site of Dover Castle and from its Saxon beginnings has served the army garrison within the castle and the surrounding area for many centuries. The church remains an army garrison church but the services are open to all.

The age of the church is uncertain but the current building dates from 800 to 1000AD (late Saxon period). However, it is likely that an earlier Roman building sat on the site, whether as a place of worship or a building to maintain the Roman lighthouse, Pharos, which lies just outside the West door. Roman building materials, especially Roman tiles, were incorporated into the walls and arches of the church by the Saxons.

At the end of the seventeenth century, church attendance dropped and soon the church fell into ruins (having been used as a fives court, coal store and rubbish dump). In 1862  the church was restored by George Gilbert Scott and later the distinctive mosaic work and other cosmetic additons were added by William Butterfield in 1889/90.

The church played a major part in the castle's history during the two world wars as a place of worship and contemplation for personnel stationed in the castle and for those heading overseas. During the spring and summer of 1940 services continued despite almost constant disruption from air-raids and anti-aircraft fire.

Today, hundreds of thousands of visitors visit the church every year as they tour around the castle. However, first and foremost, St. Mary in Castro is a working place of worship. If attending worship, an entry ticket from English Heritage is not required.