The eye which looked across the Thracian Bosphorus or the Hellespont seemed to itself to be merely contemplating the opposite bank of a pretty wide stream.

Darius, consequently being master of Asia Minor, and separated by what seemed to him so poor a barrier from fertile tracts of vast and indeed indefinite extent, such as were nowhere else to be found on the borders of his empire, naturally turned his thoughts of conquest to this quarter.

His immediate desire was, probably, to annex Thrace; but he may have already entertained wider views, and have looked to embracing in his dominions the lovely isles and coasts of Greece also, so making good the former threats of Cyrus.
The story of the voyage and escape of Democedes, related by Herodotus with such amplitude of detail, and confirmed to some extent from other sources, cannot be a mere myth without historical foundation.

Nor is it probable that the expedition was designed merely for the purpose of "indulging the exile with a short visit to his native country," or of collecting "interesting information." If by the king's orders a vessel was fitted out at Sidon to explore the coasts of Greece under the guidance of Democedes, which proceeded as far as Crotona in Magna Grsecia, we may be tolerably sure that a political object lay at the bottom of the enterprise.

It would have exactly the same aim and end as the eastern voyage of Scylax, and would be intended, like that, to pave the way for a conquest.