Full descriptions of the elements of a Gothic floorplan are found at the entry Cathedral diagram.

In Romanesque and Gothic Christian church architecture, the transept is the area set crossways to the nave in a cruciform ("cross-shaped") building. The transept separates the nave from the sanctuary, whether apse, choir, chevet, presbytery or chancel. The transepts cross the nave at the "crossing" (plan, right), which belongs equally to the main nave axis and to the transept. Upon its four piers, the crossing may support a spire, a central tower (see Gloucester Cathedral) or a crossing dome.

Since the altar is usually located at the east end of a church, a transept extends to the north and south. The north and south end walls often hold decorated windows of stained glass, such as rose windows, in stone tracery.

Some basilicas and the church and cathedral planning that descended from them, were built without transepts, but this is rare. Sometimes the transepts are reduced to matched chapels. More often the transepts will extend well beyond the sides of the rest of the building, forming the shape of a cross; this is called a "Latin cross" groundplan, and these extensions are known as the arms of the transept. A "Greek cross" groundplan, with all four extensions the same length, produces a central-plan structure with consequences for the liturgy.

When churches retain a single transept, at as Pershore Abbey, there is generally a historical disaster, fire, war or funding, to explain the anomaly. At Beauvais only the chevet and transepts stand; the nave of the cathedral was never completed after a collapse of the daring high vaulting in 1284. At St. Vitus Cathedral, Prague, only the choir and part of a southern transept were completed, until a renewed building campaign in the 19th century.

The word "transept" is occasionally extended to mean any subsidiary corridor crossing a larger main corridor, such as the cross-halls or "transepts" of The Crystal Palace of glass and iron that was built for the Great Exhibition of 1851.

In a metro station or similar construction, a transept is a space over the platforms and tracks of a station with side platforms, containing the bridge between the platforms. Placing the bridge in a transept rather than an enclosed tunnel allows passengers to see the platforms, creating a less cramped feeling and making orientation easier.

See also

• Cathedral architecture