A major problem with associating the Poieneşti-Lukashevka and Zarubintsy cultures with the Bastarnae is that both cultures had disappeared by the early 1st century AD, while the Bastarnae continue to be attested in those regions throughout the Roman Principate. Another issue is that the Poieneşti-Lukashevka culture has also been attributed to the Costoboci, a people considered ethnically Dacian by mainstream scholarship, who inhabited northern Moldavia, according to Ptolemy (ca. 140 AD). Indeed, Mircea Babeş and Silvia Theodor, the two Romanian archaeologists who identified Lukashevka as Bastarnic, nevertheless insisted that the majority of the population in the Lukashevka sphere (in northern Moldavia) was "Geto-Dacian". A further problem is that neither of these cultures were present in the Danube Delta region, where a major concentration of Bastarnae are attested by the ancient sources.