SPIELFELD, Austria — The border between Austria and Slovenia runs through Armin Tement’s backyard. Literally.

Not that you would know it. Neat rows of vines march up and down the valley like military columns with no regard for a frontier laid down by man, why here, no one can quite remember. The Slovene wine workers speak German. The Austrians speak Slovenian, or at least try.

As for the wine, well, says Mr. Tement, 32, “it tastes exactly the same on both sides.”

When Mr. Tement’s family started making wine back in the 19th century, there was no border here. The region of Styria, straddling what is now southeastern Austria and northeastern Slovenia, was part of the Hapsburg Empire.

When the empire was broken up after World War I, Upper Styria became Austrian and Lower Styria became part of Yugoslavia — until the 1990s, when that country, too, was broken up and Slovenia gained its independence.