Thousands of people who travel every day between the southern tip of Spain and the British territory of Gibraltar will no longer have to cross a physical border.
The official opening at midnight on Tuesday - after a border fence was fully removed - allows a new freedom of movement under a historic treaty between the European Union and the United Kingdom that came after years of post-Brexit wrangling.
The contested British Overseas Territory of 38,000 people is perched at the southern tip of the Iberian Peninsula, strategically located mere kilometres from Morocco at a point where the Atlantic Ocean meets the Mediterranean Sea.
When Britain left the EU in 2020, the relationship between Gibraltar and the bloc was left unresolved.
Previous talks on a deal to ensure people and goods could keep flowing across the border had made halting progress. In 2025, the EU and UK announced an agreement on those issues, with the two sides and Gibraltar's government signing a treaty Tuesday that eases border crossings.
The UK's Foreign Office Minister Stephen Doughty said on Tuesday the agreement secured Gibraltar's long-term economic future and interests.
Maroš Šefčovič, the EU's trade representative, praised the agreement, too.
"It has taken four years of patient, complex negotiation, but the outcome speaks for itself," Šefčovič said.
"It is a very special feeling to see a fence come down."
Without a deal, Gibraltar could have a faced a hard land border with full passport checks, posing economic risks for the territory deeply dependent on some 15,000 Spaniards - almost half of Gibraltar's workforce - who cross the frontier every day for work.
Leisure visits by people crossing both sides of the border would have been affected, too.
"People who are visiting family in Spain, or whose Spanish family is visiting them in Gibraltar. Children who are going to football matches and extracurricular activities, either in Spain or in Gibraltar. They will be able to do that without having to worry about frontier queues," Gibraltar's Chief Minister Fabian Picardo told The Associated Press.
The deal in effect brings the territory into the EU's Schengen free travel area.
At Gibraltar's airport and port, entry and exit checks will be conducted by both UK and Spanish border officials. The arrangement is similar to what's in place at Eurostar train stations in London and Paris, where both British and French officials check passports.
In Britain's 2016 Brexit referendum, 96 per cent of voters in Gibraltar or the Rock, as the territory is popularly known in English, supported remaining in the EU.
Travellers to Gibraltar from countries outside the Schengen area will have to contend with the EU Entry-Exit System, or EES, that was rolled out in Europe in April and replaced passport stamps with biometric data collected through photographs and digital fingerprints.
Gibraltar was ceded to Britain in 1713, but Spain maintains its sovereignty and the treaty that removed the border fence does not resolve the territory's contested status.