There were ecstatic scenes as Eritreans and Ethiopians poured across their common border, as their leaders formally opened it.
President Isaias Afwerki and Prime Minister Abiy Ahmed officially opened the Debay Sima – Burre border to allow road transport and then headed for the Serha-Zalambesa crossing point.
But as ordinary people cross, hug and cry as they meet family and friends they have been separated from for years, its important to ask one simple question: how will the border peoples be treated in the years ahead?
Look carefully at this BBC map of the border. Plenty of land that will have to be moved from one country to another. Eritrean villages are due to find themselves in Ethiopia. And Ethiopian villages will be in Eritrea.
But how will this be done?
It is vitally important that as land is swapped people do not become stateless.
How will the citizenship of people who are moved from one nation to another be protected? Will they be allowed to keep their existing citizenship? It would be possible to allow this. Or they could be given the citizenship of both countries.
Whose police will deal with ordinary village disputes? Who will village leaders report to – their old regional offices, or those of their new nation?
I have no answer to these questions: but they need to be answered – sharpish!