This contribution examines the plans of the Athenians and their allies at the
foundation of the Delian League in 478 by exploring conjectural force structures. Likely
Persian forces of c. 600 triremes could be anticipated. Persia had also demonstrated
noteworthy capacity to mount closely successive expeditions and to recover from losses.
Therefore, the Delian League was severely challenged to match ship for ship and to find
the requisite manpower. Various methodologies yield both total and practicable allied
fleets of different sizes (with total hulls touching 600 at highest estimate). Financial administration
and tactical deployment discouraged small ship contingents for the allies in
favor both of levying monetary tribute which funded the Athenian fleet and of manning
its ships with personnel from smaller maritime allies. Hypotheses on the costs of allied
forces can be proposed in order to understand the high initial Aristeidian assessment of
the allies. Eurymedon represents a turning point, demonstrating how early preemptive
deployment and confrontation far eastward from the Aegean by the Delian League
compensated for superior Persian resources.