Derry/Londonderry (Northern Ireland), Mar 19 (efe-epa).- On maps of Ireland, a line cuts across the north of the island like a scar, dividing Northern Ireland from the larger Republic of Ireland.
That line is both physical and symbolic, signaling the geographic separation of two countries as well as their historical, social and religious differences.
After Mar. 29, 2019, the thin line could well separate the United Kingdom and the European Union.
The reality of the Irish border is complex.
Today, it is no longer a "hard" border, though crossings are littered with rusting customs posts from another time.
Often a change in road markings or the color of the tarmac are the only indicators that you have crossed into another nation.
It is possible to drive along a road and cross the border two or three times without even knowing it.
The border, which stretches 499 kilometers (310 miles), was established in 1921 by the Anglo-Irish Treaty whereby 26 Catholic counties were granted autonomous status as the Republic of Ireland and six northern counties, inhabited mostly by Protestants loyal to the British monarchy, remained within the UK as Northern Ireland.
The division of the island and the discrimination of the Catholic population in Northern Ireland led to a conflict between republican militias, mostly Catholics calling for union with the rest of the island, and unionist paramilitaries from largely Protestant areas who wanted to remain part of the UK.
Decades of political violence, known as The Troubles, which began in the late 1960s and continued until the signing of the Good Friday Agreement in 1998, cost the lives of more than 3,000 people.
After the signing of the international peace deal, bloodshed fell considerably, bringing an end to the need for fences and border barriers, and Irish citizens were able to move freely around the island.
Every day, about 30,000 citizens cross the border, which can be intersected at some 275 points.
Brexit, the UK's withdrawal from the EU, slated for Mar. 29, could disrupt a delicate balance on the island of Ireland, threatening to bring back controls and border posts, symbols of a bygone Irish conflict, which could become targets for paramilitary groups like the Irish Republican Army (IRA), whose sympathizers still long for the reunification of the island.
Although the Irish backstop, a mechanism agreed as part of UK Prime Minister Theresa May's deal with the EU aimed at avoiding a hard border, is a central part of Brexit, many who live along the border feel that UK voters did not consider the implication when they cast their ballots in the 2016 referendum on leaving EU membership.
Many living on the frontier will only talk about Brexit off the record and do not want to cause trouble with their neighbors.
Populations that straddle or are near the border, such as the city of Derry, also known as Londonderry, are still socially divided.
Curbs and lampposts are painted in the colors of the Union Jack or Irish flags, and pro-IRA slogans are displayed prominently in tribute to those who died in The Troubles.
Residents of the divided villages have memories of the border, where customs checks were circumvented by entrepreneurial traders.
Some predict that areas like Lough Macnealan, on a remote part of the southwestern edge of the border, will become a smuggler's paradise after Brexit.
Though the border is invisible, it resonates with significance.
It is a testament that individuals can move on from the past and overcome social and political differences. It also stands as a stark warning from history to guard against future conflict bubbling under the surface.
Unless a solution is found to Brexit, then the Irish border will be a scar that may be impossible to heal.