Herodotus (c.484–c.425 BCE) was a Greek historian often called the “Father of History” (in European terms). He collected materials about various peoples, traveling widely through the Mediterranean and Black Sea regions, and wove them together into an historical narrative. Herodotus may have borrowed from Hecataeus. The “Carpis” and “Alpis” seem to be tributaries of the Danube river which flow down from the Carpathian Mountains and Alps respectively.
The following is an adaptation of Herodotus, trans. A. D. Godley. Cambridge: Harvard University Press, 1920.
§ 2.33. […] the Ister [Danube] emerges from the land of the Keltoi at Pyrēnē and flows through the very middle of Europe; now the Keltoi live beyond the Pillars of Heracles, being neighbors of the Kunēsioi, who are the westernmost of all the peoples inhabiting Europe. The Ister, then, flows clean across Europe and ends its course in the Euxine sea, at Istria, which is inhabited by Milesian colonists.
§ 4.49. […] The Carpis and another river called Alpis also flow northward, from the country north of the Ombrici, to flow into it [the Danube]; for the Ister [Danube] traverses across the whole of Europe, emerging among the Keltoi, who are the most westerly dwellers in Europe, except for the Kunētes, and thus flows across Europe it comes to the borders of Scythia.