Identity checks at the borders of Bulgaria and Romania have been abolished, opening up free travel to the European Union.
Romania and Bulgaria have become full members of the Schengen area, expanding the border-free zone to 29 members and ending a 13-year wait for the two Eastern European countries.
The expansion, which was made possible when Austria and other members dropped objections to the former communist countries joining, took place at midnight (22:00 GMT) on Wednesday, marked by customs at various borders.
Identification checks at the border between Bulgaria and Romania and the neighboring countries of the European Union officially stopped at midnight, giving travelers the freedom to enter 27 other countries.
Two Balkan countries partially integrated Schengen area in March, but free travel was only for those arriving by air or sea.
Late on Tuesday, the interior ministers of Bulgaria and Romania met at the Ruse-Giurgiu border between the two countries to mark the opening of the border. A short ceremony was held at the Hungarian-Romanian border with a meeting between the head of the Hungarian police and the head of the Romanian border police.
Romania and Bulgaria joined the EU in 2007, but were not included in the borderless zone until March, when border checks were lifted for sea and air travel. Land border checks remained in place amid opposition, particularly in Austria, amid concerns that the two countries were not doing enough to stop illegal immigration.
The the size of the Schengen Area it came after months of efforts to include Bulgaria and Romania in Hungary's state during its six-month EU presidency.
About a million Hungarians live in Romania's Transylvania region, a legacy of Hungary's post-World War I partition. Relations have been tense between the two countries, but opening the border will ease travel and strengthen ties between the regions.
Schengen, one of the main successes of the European project, was established in 1985 as an intergovernmental project between the five EU countries – France, Germany, Belgium, the Netherlands and Luxembourg. It has gradually grown into the largest free travel destination in the world.
However, several Schengen member states, including the Netherlands, Austria and Germany, this year reintroduced border checks on issues ranging from immigration to security. Some EU officials warned that the bounced checks could undermine the policy's objectives.
Before Bulgaria and Romania partially acceded, Schengen included 23 of the 27 EU member states, along with Switzerland, Norway, Iceland and Liechtenstein. About 3.5 million people cross internal borders every day, and more than 420 million people live in the Schengen area.