It was by successive proceedings of this sort that many detachments of Athenian citizens became settled in various portions of the maritime empire of the city,—some rich, investing their property in the islands as more secure—from the incontestable superiority of Athens at sea—even than Attica, which, since the loss of the Megarid, could not be guarded against a Peloponnesian land invasion,[18]—others poor, and hiring themselves out as laborers.[19] The islands of Lemnos, Imbros, and Skyros, as well as the territory of Estiæa, on the north of Eubœa, were completely occupied by Athenian proprietors and citizens,—other places partially so occupied. And it was doubtless advantageous to the islanders to associate themselves with Athenians in trading enterprises, since they thereby obtained a better chance of the protection of the Athenian fleet. It seems that Athens passed regulations occasionally for the commerce of her dependent allies, as we see by the fact, that shortly before the Peloponnesian war, she excluded the Megarians from all their ports. The commercial relations between Peiræus and the Ægean reached their maximum during the interval immediately preceding the Peloponnesian war: nor were these relations confined to the country east and north of Attica: they reached also the western regions. The most important settlements founded by Athens during this period were Amphipolis in Thrace, and Thurii in Italy. [18] Xenophon, Rep. Ath. ii, 16. τὴν μὲν οὐσίαν ταῖς νήσοις παρατίθενται, πιστεύοντες τῇ ἀρχῇ τῇ κατὰ θάλασσαν· τὴν δὲ Ἀττικὴν γῆν περιορῶσι τεμνομένην, γιγνώσκοντες ὅτι εἰ αὐτὴν ἐλεήσουσιν, ἑτέρων ἀγαθῶν μειζόνων στερήσονται. Compare also Xenophon (Memorabil. ii, 8, 1, and Symposion, iv, 31). [19] See the case of the free laborer and the husbandman at Naxos, Plato, Euthyphro, c. 3.