A portal is the covered architectural space that, in some buildings or blocks of houses, is arranged in front of the entrances to protect from rain and cold,[1]​ allowing pedestrian traffic.

Its shape is that of a porch, gallery "Gallery (architecture)") or elongated portico; although it is not limited to the main entrance (as happens in porches and atriums). The arcades run along the entire façade of one or more buildings; and in the case of supported streets or arcaded[2]​ they continue along the entire length of the street, often on both sides.

They are very common in Spanish rural architecture and have characterized the commercial streets (Calle Mayor) of the historic center of some cities (Alcalá de Henares, Palencia) since the Middle Ages. When they do not respond to a planned design (many of them are even the result of spontaneous self-construction, which makes the houses grow organically over generations), there is no unity in their dimensions and appearance (for example, in the multiplicity of supporting elements - columns "Column (architecture)"), pillars "Pillar (architecture)") or uprights-). Some are linteled and others vaulted, or supported by galleries of arches "Arch (architecture)") (arches or arcades).

The main squares are also usually supported. Its connection to the commercial function (particularly appropriate to the possibility of keeping goods protected from rain and sun) is even reflected in the DRAE: Portico, like a cloister, that some buildings or blocks of houses have on their facades and in front of the doors and shops that are in them.[1]​ This definition also points out the formal similarity with monastic cloisters, which they also maintain with the patios of Muslim mosques. A covered religious space that also had civil functions, as a meeting space in front of the council churches, was the atrium or portico of certain medieval Spanish churches.

Precedents of medieval arcades were the of Greek Antiquity.[5]​ In Italy the space called is similar. The of Venice (since 1177) includes supported structures on three sides, as does the of Vigevano "Piazza Ducale (Vigevano") (Ambrogio da Corte") and Bramante, 1492-1494). In the of Pienza (Bernardo Rosellino"), 1458-1464) only The corner corresponding to the was supported. The Italian city of Bologna is famous for the length of its porticoes. In total, there are more than 45 kilometers on its facades, approximately 38 in the city center. What can be considered the longest arcade in the world is the so-called , which measures approximately 3.5 kilometers, and leads from the city to the Sanctuary of the Madonna di San Luca. Similar are the classical and baroque colonnades, such as Bernini's in St. Peter's Square.