Coordinates: 34°38′12″N 5°31′22″E / 34.636598°N 5.522904°E / 34.636598; 5.522904 Gemellae was a Roman fort and associated camp on the fringe of the Sahara Desert in what is today part of Algeria. It is now an archaeological site, 25 km south and 19 km west of Biskra, and 5 km southwest of the present-day village of M'Lili with which it probably shares an original Berber name.

Apparently there was a fortification at Gemellae prior to the coming of the Romans. Pliny the Elder recounts that when Lucius Cornelius Balbus celebrated his victory over the Garamantes of the Sahara in 19 BCE, one of the conquests feted in the parade through Rome was that of Milgis Gemmella, described as an oppidum (usually meaning fortified settlement).

The Romans seem to have then occupied the site and made it one of southernmost outposts, marking the limes or boundary of the Empire.

The earliest epigraph retrieved from the site is an inscription for a statue of Emperor Hadrian, in about the year 126 CE, by a cohors equitata (equestrian regiment) originating from Chalcis in Syria. The presence of this army unit in Africa is attested by inscriptions elsewhere dating from as early as 78 CE and as late as 164 CE.