Do you want one that has been fixed in place for the longest time?

If so, the Swedish-Norwegian border (which remained even when the countries were in a Union 1814-1905) has been the same since 1660.

Portugal has had the same borders since about 1300, but the states on the other side of the border has gone from Catile to Spain. Spain and Portugal were also in a Union 1580 to 1640.

The borders of Andorra do not appear to have changed since its creation in 988.

Depends somewhat what you let count as a land border. The one between Scotland and England has been (up to a few minor things like Berwick) fixed de jure since 1237 and de facto for much longer. That seems a reasonably strong contender.

This one will be tough to answer, as nobody is an expert in every country's history.

We should start by defining some rules that I believe are in the spirit of your question.

• National border (not a state/county etc).

• Exception to above: when a national border becomes a non national border for a period, but stays defined and reverts to a national border (eg Sweden and Norway).

• Land border (Australian mainland hasn't changed much in Millennia).

I suspect our answer is going to be in Europe, and probably fairly recent (past 500-800) years.

I hope our historians can answer it. It's a great question.

Does anyone know if the Swiss borders have changed much over time? It would seem that without armed conflict, the chance of gaining or losing land is low.

The border between the Ottoman Empire/Turkey and the Safavid Empire/Iran has remained relatively unchanged since the early 1500s.