Altar Position

The Church of St. Peter

In some churches, why is the altar fixed to the sanctuary wall so that during the Eucharist the priest stands in front of the altar with his/her back to the congregation?

Until the early part of the fourth century, Christian worship was prohibited by Roman law and Christians were forced to gather secretly in private homes. When they celebrated the Eucharist, they probably stood around the dining room table, with the priest or bishop leading the worship.
In the Middle Ages, when Christianity flourished and many of the great cathedrals of Europe were built, there was an increasing sense of the priest as mediator between the people and God. As a result, altars were pushed against the wall and became fixed and immovable. The priest stood between the altar and the people, offering the sacrifice of the mass on their behalf.
During the Reformation, there was an attempt to recapture the image of the Lord's Supper, where the community shared the sacramental meal together. Within Anglicanism, this continued into the twentieth century with a renewed understanding of the priest as the presiding celebrant among the many celebrants in the liturgy. As a result, most altars in Anglican churches were pulled back from the wall and became free-standing, with the priest behind the altar and the community gathered around.
Some churches in our diocese have chosen to leave their altars "eastward facing" (against the wall), although this is now an exception rather than the norm.