Greek and Turkish Cypriots have reopened a major crossing in the divided Cypriot capital of Nicosia.
Ledra Street, which had come to symbolise the partition of the island, was declared open by local officials.
It was then closed again for a couple of hours by the Greek Cypriots, after what they called an illegal Turkish Cypriot police patrol.
The crossing was finally re-opened later on Thursday evening after mediation by UN officials.
Protesters had gathered on both sides of the barrier, chanting "Cyprus belongs to its people", after the street had been closed again.
"After consultations with the UN, we have been given assurances that this will not happen again," Kypros Michailidis, Nicosia's Greek Cypriot police chief, told the Associated Press news agency.
Ledra Street was divided in 1964, during a flare in violence between the ethnic Greek and Turkish communities.
New Cypriot President Demetris Christofias and Turkish Cypriot leader Mehmet Ali Talat had agreed to reopen the busy shopping street last month.
The two leaders have also agreed to resume talks on reunifying the island.
Earlier, as the street reopened, an aide to Mr Talat, Osdil Nami said: "We are living a historic day today. We are witnessing one of the obstacles to a solution come down."
EU Enlargement Commissioner Olli Rehn also welcomed the reopening, saying it showed that the two sides were "ready to put aside the difficulties of the past".
Greek and Turkish Cypriots have been divided since 1974, when Turkey deployed troops after a coup by Greek Cypriots who wanted union with Greece.
Ledra Street had been at the centre of the island's leading shopping district before it was blocked in the middle, with military posts either side of the dividing line.
Cyprus' government demolished a wall and military checkpoint on Ledra Street last year.
But plans to reopen the street were rejected by President Christofias' predecessor, Tassos Papadopoulos.
"We still have a long way to go," said the mayor of Nicosia, Eleni Mavrou. "This is the first step. We hope many more will follow."
It has been a long time coming! There used to be a day when all of us in Cyprus were brothers, and hopefully that day will return again soon.
Mehmet Brinjikji, Nicosia, Cyprus
I have just walked along the formerly forbidden part of Ledra Street. It was a strange, shivering sensation. Being a soldier there 10 years ago I would never have imagined this moment back then. Yet this is reality and I am very positive better days will follow.
Constantinos, Nicosia, Cyprus
I am studying at the University of Nicosia for a semester and got to cross the border today. It was a festive attitude during most of the time and people were very friendly and excited about the change. I feel blessed to have been able to take part in this significant event in Cypriot history.
Kelly Juranek, Walworth, WI
Having seen what we achieved today in Ledra Street proves that if "we", the people of Cyprus, want to achieve good things together, we would. This is a very positive sign towards reunification of our island. I believe it is also raising hopes of youngsters, like me, who are away from the homeland for various reasons. We have to be optimistic, and be proactive for our own island, and not make the same mistakes that we did in the past - for instance, waiting for other nations to find a solution for us.
Hulusi Kilim, Bath, UK (Famagusta, Cyprus)
As a cypriot that grew up in Cyprus and then moved to London I see this as a positive step. Cyprus is too small to be divided. If people here in the most cosmopolitan city in the world, including greek and turkish cypriots, live in harmony, why can't people on the island?
Michael Nicolaou, London
In my opinion the green line should be "erased" a long before today! This is a huge step in the history of Cyprus and I think it is an anticipation of what is coming next. Try to think positive for the following days.
Kyriaki Yiakoupi, Nicosia,Cyprus
Had it been happening years ago, the opening would have meant much more. Today, as a rare event, both sides actually agreed on something, despite this opening we are still far away from a complete settlement. It is also very disheartening for me, as a young Turkish Cypriot, to read some of these comments. While I am used to the negative comments from both communities almost to the point of immunity, I always wonder what will happen to us if there is a miraculous solution? Where will all these negative feelings go?
Adil Seytanoglu, Sheffield, South Yorkshire (Originally Nicosia)
The division in Cyprus will continue until attitudes of the Greek Cypriots toward the Turkish Cypriots soften, perhaps then both Greek and Turkish troops can leave the island.
Jon Smith, Saxmundham, Suffolk
What the Greeks are doing is giving forgiveness to the Turkish occupiers.
Nicolas Makrides, Nicosia
I am an American Cypriot. This is a very big step forward. When you used to walk at Ledras you would see barbed wire and soldiers with machine guns. It was very frightening. We always had to be careful not to make a mistake and cross the green line (imaginary). Many people had made the mistake of crossing (without realising it) and then having to go through the hassle of explaining it was a mistake. I can't wait to see Ledras when I go in June.
Christine Skoumbris, Lakewood, Ohio USA
Having spent three years as a former member of HM Forces in Cyprus, I think that this is the best news for some considerable time. The only divisive area now will be reclamation of land lost during the war. This will need to be handled with kid gloves.
John Davidson, Cleckheaton, West Yorkshire
The atmosphere in Cyprus has become much more positive towards finding a solution since the new president was elected. For efforts to succeed it will need grassroots support from the people on both sides of the island. Today's event is a very symbolic example of how that can be developed. There is still a long way to go, but compared to the negativity and hostility which prevailed just a few weeks ago, it's a very big step in the right direction!
Martin Standage, Paphos, Cyprus
This "opening" means absolutely nothing. It is a "firework" which destructs attention of public opinion in Cyprus and abroad from the real cause of the division of Cyprus which is nothing else than the continuous presence of Turkish troops.
Konstantinos Koudounas, Nicosia, Cyprus