A lintel (from lintel,[1]​ and this from the Latin limitellus)[2]​[3]​ is a horizontal structural element that bridges a space between two supports or jambs.[3]​.

It is the upper element that allows creating openings in the walls to form doors, windows or porches. By extension, the type of architecture, or construction that uses lintels to cover spaces in buildings is called lintel architecture or lintel construction. The one that uses arches "Arch (architecture)") or vaults is called vaulted architecture.

The best exponents of lintel architecture in stone are the monumental buildings of Ancient Egypt, classical Greece and in many examples of classical Rome.[3]​ It is considered a static element in architecture compared to the vaulted one, considered dynamic.[3]​.

It is known as a transdosado lintel when it is a flown lintel. A horizontal piece that is protruding from a wall plane, as if it were a balcony, although it is not.

In a lintel whose ends fall on the vertical elements whose free space spans the lintel, the greatest stresses will occur on the central cross section. In this case, the stress on the lintel, if it has a small depth in relation to the length, can be calculated from the Euler-Bernouilli beam theory for the mechanical bending of beams (if the depth is appreciable in relation to the length, Stephen Timoshenko's theory must be used, which also considers the effect of shear stress). In the previous case, flexion causes the upper part to be compressed and the lower part to be pulled.

Rigid materials such as stones (mass concrete and other ceramic-type materials) withstand tensile stresses worse than compression stresses, which is why the most common pathology in stone lintels are cracks that arise from the bottom of the lower face and progress to the top. A traditional solution to this problem was the replacement of the lintels with "Arch (architecture)" arches, which allow the load of the upper floor to be supported by subjecting the material only to compression forces.

Advances in construction materials have, however, made it easier to use lintels. Reinforced concrete corrects the problem with steel reinforcement at the bottom that absorbs tensile stresses. Hence, lintel structures (of beams and pillars) are now common with this material, without any of the problems that structures of this type had before, with much larger free spans.