In architecture, a boss is a knob or protrusion of stone or wood.
Bosses can often be found in the ceiling

Ceiling

A ceiling is an overhead interior surface that covers the upper limit of a room. It is generally not a structural element, but a finished surface concealing the underside of the floor or roof structure above....

s of buildings, particularly at the intersection of a vault

Vault (architecture)

A Vault is an architectural term for an arched form used to provide a space with a ceiling or roof. The parts of a vault exert lateral thrust that require a counter resistance. When vaults are built underground, the ground gives all the resistance required...

. In Gothic architecture

Gothic architecture

Gothic architecture is a style of architecture that flourished during the high and late medieval period. It evolved from Romanesque architecture and was succeeded by Renaissance architecture....

, such roof bosses (or ceiling bosses) are often intricately carved with foliage, heraldic devices

Heraldry

Heraldry is the profession, study, or art of creating, granting, and blazoning arms and ruling on questions of rank or protocol, as exercised by an officer of arms. Heraldry comes from Anglo-Norman herald, from the Germanic compound harja-waldaz, "army commander"...

 or other decorations. Many feature animals, birds, or human figures or faces, sometimes realistic, but often grotesque: the Green Man

Green Man

A Green Man is a sculpture, drawing, or other representation of a face surrounded by or made from leaves. Branches or vines may sprout from the nose, mouth, nostrils or other parts of the face and these shoots may bear flowers or fruit...

 is a frequent subject.

Bosses were also an important feature of ancient and Classical

Classical architecture

Classical architecture is a mode of architecture employing vocabulary derived in part from the Greek and Roman architecture of classical antiquity, enriched by classicizing architectural practice in Europe since the Renaissance...

 construction. When stone components were rough-cut offsite at quarries, they were usually left with bosses (small knobs) protruding on at least one side. This allowed for easy transport of the pieces to the site; once there, the bosses also facilitated raising and/or inserting them into place. An excellent and still extant example of such bosses can be seen at the Greek Doric

Doric order

The Doric order was one of the three orders or organizational systems of ancient Greek or classical architecture; the other two canonical orders were the Ionic and the Corinthian.-History:...

 temple of Segesta

Segesta

Segesta was the political center of the Elymian people, located in the northwestern part of Sicily, in what are now the province of Trapani and the comune of Calatafimi-Segesta....

, at which construction was never completed. The bosses of several key elements of the temple, notably the crepidoma

Crepidoma

Crepidoma is an architectural term related to ancient Greek buildings. The crepidoma is the platform of, usually, three levels upon which the superstructure of the building is erected. The levels typically decrease in size incrementally, forming a series of steps along all or some sides of the...

, remain as a testament to the construction process.