Atuatuca (or Aduatuca) is the name of two ancient fortified settlements located in the eastern part of modern Belgium, between the Scheldt and Rhine rivers. The oldest one, Atuatuca Eboronum, attested during the Gallic Wars (58–50 BC), was the stronghold of the Eburones. The other one, Atuatuca Tungrorum (modern Tongeren), founded around 10 BC, was the Roman-era capital of the Civitas Tungrorum, inhabited by the Tungri.

The place name Atuatuca is first mentioned in the mid-first century BC by Julius Caesar to designate the stronghold of the Eburones: "...he [Caesar] concentrated the baggage of all the legions at Aduatuca. That is the name of a fort (castellum) situated almost in the middle of the territory of the Eburones."

Whether Atuatuca or Aduatuca is the original form is uncertain. In the earliest surviving manuscript of Caesar's Gallic War, dated to the early 9th c. AD, the name is given as Aduatuca. The reason for the spelling variation has been debated. Maurits Gysseling has proposed that Atuatuca was the original form, which later gave way to Aduatuca under the influence of Romance languages. Lauran Toorians argues on the contrary that the original Gaulish prefix ad- was changed to at- as the result of a hypercorrection by medieval copyists, who may have thought that the ad- form had emerged under the influence of the Old French phonology during the first millennium AD.

The ancient name of the city of Tongeren, founded ex-nihilo by the Romans around 10 BC, is rendered as Atuatuca Tungrorum on the basis of written sources from the beginning of the Common Era: the settlement is known as Atouatoukon ca. 170 AD (Ptolemy), Tungri in the late 4th c. AD (Ammianus Marcellinus), civitas Tungrorum (Notitia Galliarum), Aduaga Tungrorum (Antonine Itinerary), and as Atuaca (Tabula Peutingeriana).

The meaning of the name Atuatuca remains unclear. According to Xavier Delamarre, it may be formed with the Gaulish suffix ad- ('towards') attached to the stem uātu- ('Vāti, soothsayer, seer, prophet') and the suffix -cā (most likely a feminine variant of -āco-, denoting the provenance or localization). An original Gaulish form *ad-uātu-cā ('place of the soothsayer, where one goes to prophesy') has thus been proposed.

The meaning 'the fortress' has also been postulated by Alfred Holder in 1896, by reconstructing the name in Gaulish as *ad-uatucā and comparing the second element to the Old Irish faidche ('the free place, the field near a dún [fortress]' < *uaticiā). This proposition has been debated as linguistically untenable in recent scholarship.

The name Atuatuci, borne by a Gallic-Germanic tribe dwelling near the Eburones, is linguistically related to the place name Atuatuca, although the settlement cannot be historically linked to the tribe with certainty. Willy Vanvinckenroye has argued that the Eburones did not have their own strongholds and used instead the fortress of the Atuatuci to house troops since they were tributary to them.

The exact location of Eburonean stronghold remains uncertain, but it is almost certainly not the same as Tungrorum since no evidence of human settlement before the end of the first century BC have been found there. The location of the stronghold has been highly debated among scholars since the middle of the 20th century. In the words of Edith Wightman, "changes which took place after Caesar, involving new folk from across the Rhine and reorganization of existing peoples, make localization difficult."