In Romanesque , Byzantine and Gothic Christian abbey , cathedral and church architecture , the term is applied to a semi-circular or polygonal termination of the main building at the liturgical east end ( where the altar is ) , regardless of the shape of the roof , which may be flat , sloping , domed , or hemispherical .
In Romanesque , Byzantine and Gothic Christian abbey , cathedral and church architecture , the term is applied to a semi-circular or polygonal termination of the main building . This is usually at the liturgical east end ( where the altar is ) .