Algeciras (alxeˈθiɾas) is a municipality of Spain belonging to the province of Cádiz, Andalusia. Located in the southern end of the Iberian Peninsula, near the Strait of Gibraltar, it is the largest city on the Bay of Gibraltar (Bahía de Algeciras). The Port of Algeciras is one of the largest ports in Europe and the world in three categories: container, cargo and transshipment. The urban area straddles the small Río de la Miel, which is the southernmost river of continental Europe. As of 1 January 2020, the municipality had a registered population of 123,078, second in its province after Jerez de la Frontera and greater than Cádiz city population. It forms part of the comarca of Campo de Gibraltar.
The surrounding metro area also includes the municipalities of Los Barrios, La Línea de la Concepción, Castellar de la Frontera, Jimena de la Frontera, San Roque and Tarifa, with a population of 263,739.
The Arabic name for the settlement founded by Muslims after the conquest of the Iberian Peninsula was al-Jazīrah al-Khaḍrāʾ (الجزيرة الخضراء, "The Green Island"), in reference to Isla Verde. Al-Jazīra(t) gave the modern Spanish Algeciras. Algeciras' site was also that of Roman cities called Portus Albus ("White Harbor"), Caetaria (current Getares) and Iulia Traducta. In the later "Byzantine" period, the site would come to be known in Greek as Mesopotámenoi (Μεσοποτάμενοι), meaning "between rivers/canals".
The area of the city has been populated since prehistory, and the earliest remains belong to Neanderthal populations from the Paleolithic era.
Due to its strategic position it was an important port under the Phoenicians, and was the site of the relevant Roman port of Portus Albus ("White Port"), with two nearby cities called Caetaria (possibly founded by the Iberians) and Iulia Traducta, founded by the Romans.
Recently it has been proposed that the site of Iulia Transducta was the Villa Vieja of Algeciras.
After being destroyed by the Goths and their Vandal allies, Tarik landed in Algeciras and Tarifa in April 711.