the Peloponnesian League who were getting the worst of an ongoing border dispute with their Corinthian neighbors (Thuc. 1.103.4). Megara’s strategic location on the narrow isthmus joining the Peloponnese to central Greece was not lost on the Athenians, who immediately connected Megara and its port of Nisaea on the Saronic Gulf with protective walls, which they garrisoned with their own troops (Thuc. 1.103.4). Not only was this overtly expansionist activity around the isthmus threatening to the Corinthians in particular (Thucydides 1.103.4 influentially identifies it as the “original cause of the extreme hatred” of Corinth for Athens7) but the Athenian control of Megara prevented the Spartans from leading troops out of the Peloponnese by land into central Greece.8 This blatant Athenian attempt to extend their sphere of influence provoked a series of open conflicts with the Spartans and their Peloponnesian allies (especially Corinth), conventionally but somewhat misleadingly known as the First Peloponnesian War (Lewis 1997, 72).
In the opening engagement, the Athenians attempted to counter Corinthian ambitions in the eastern Peloponnese by attacking the port town of Halieis on the Argolic gulf (possibly on behalf of their new ally Argos, but almost certainly also to consolidate their own control of the Saronic Gulf),9 where they were defeated in a land battle by the Corinthians, Epidaurians, and Sicyonians (Thuc. 1.105.1, with SEG 31.369). Despite this inauspicious beginning, the Athenians defeated the Peloponnesians soon afterward in a sea battle off the small island of Cecryphalea just west of Aegina (Thuc. 1.105.1) and followed up this victory with a decisive defeat of the powerful Aeginetan fleet (along with their Peloponnesian allies), which enabled them to lay siege to Aegina (Thuc. 1.105.2), the large island that was their longtime rival in the Saronic Gulf. The Corinthians attempted to aid the Aeginetans by sending forces to attack Megara, assuming that with so many troops committed overseas in the Egyptian expedition the Athenians would be forced to withdraw from Aegina (Thuc. 1.105.3). The Athenian general Myronides defied expectations by leading the reserve troops (that is, those considered too young or too old for active duty) to Megara, where they defeated the Corinthians first by a narrow margin and then more decisively in a second battle culminating in the massacre of their retreating foes (described vividly by Thucydides 1.106.1–2).10 Despite their initial success, the Athenians were sufficiently nervous of a possible Peloponnesian invasion by land that they began to construct the Long Walls linking the city to the Piraeus in order to ensure that Athens could not be cut off from the sea (Thuc. 1.107.1).
It is at this point that Thucydides records the Spartans as openly entering the conflict for the first time,11 sending an army to liberate their mother city of Doris in central Greece from the Phocians (Thuc. 1.107.2).12 Although Thucydides (1.107.3) tells us that after their expulsion of the Phocians the Spartan forces were prevented from returning home by land and by sea (thanks to Athenian control of the isthmus and the Corinthian Gulf) and therefore decided to cross into Boeotia instead, it is far more likely that the Spartans’ actual intention was to build up the Theban army (in return for support of Theban hegemony over Boeotia) as an effective force against Athens beyond the isthmus.13 The Athenians, wary of the danger presented by a Spartan–Boeotian rapprochement (particularly in light of overtures to the Peloponnesians by political opponents of the democracy in Athens, if Thucydides 1.107.4–6 can be believed), sent a large army to fight at Tanagra, but were no match for the Spartans on land (Thuc. 1.108.1). Two months later, the Athenians under Myronides retaliated by marching north and defeating the Boeotian army at Oenophyta, which left them in control of much of central Greece (Thuc. 1.108.2),14 and soon afterward of the Saronic Gulf as well, through their reduction of Aegina (Thuc. 1.108.4).
This aggressive policy of expansion culminating in the Athenian acquisition of a land empire could not be sustained indefinitely, particularly with the ongoing large-scale naval campaigns against the Persians in the eastern Mediterranean, and the Athenians soon suffered a series of reverses (Thuc. 1.109–111), prompting them to sign a five-year truce with the Peloponnesians (Thuc. 1.112.1).15 During the period of the truce, the only recorded conflict between the Spartans and the Athenians occurred indirectly over control of Delphi.16 Upon its conclusion, the Boeotians lost no time in exploiting Athenian vulnerability by revolting, and an Athenian army was defeated at Coronea, forcing the Athenians to withdraw from all of Boeotia (Thuc. 1.113). The uprising in Boeotia was soon followed by the revolts of both Euboea and Megara, and the Spartan invasion of Attica (Thuc. 1.114). The Athenians had no choice but to give up any formal claims to a land empire (not only central Greece, but all of their land outposts in the Peloponnese) in the Thirty Years’ Peace they signed with Sparta in 446/445 (Thuc. 1.115.1),17 the terms of which cemented the division of the Greek world into two great power blocs, Athens exercising hegemony by sea and Sparta by land.18
The Peloponnesian War (431–404)
Despite the mutual recognition of separate spheres of influence, the Thirty Years’ Peace did not dissolve the tension that existed between Sparta and Athens. Although the terms of the peace allowed Athens a free hand in their brutal suppression of the Samian revolt in 440/439,19 by the mid-430s a series of disputes broke out—Thucydides’ “openly acknowledged grievances” (1.23.6), especially between Athens and Corinth, Sparta’s most powerful and aggressive ally. Open warfare between Corinth and its disaffected colony of Corcyra led to the Corcyraeans approaching the Athenians with a request for a defensive alliance. As a neutral state, they were permitted by the terms of the Thirty Years’ Peace to join either the Spartan or the Athenian bloc (Thuc. 1.35.2, 1.40.2), and the Athenians had their eyes upon their large navy, especially as they were well aware that war was in the air.20 Inevitably, however, the Athenian acceptance of this defensive alliance resulted in open warfare between Athenian and Corinthian ships in the Battle of Sybota in 433 (Thuc. 1.47–54). In the aftermath of the battle, the Athenians became concerned about the continued loyalty of Potidaea, a city in the Chalcidice, an area crucial for Athenian economic and military interests. Although Potidaea was a tribute-paying member of the Delian League, it was also a Corinthian colony that maintained a very close relationship with its mother city. When the Athenians demanded that they tear down a portion of their fortification walls, send hostages, and sever their official ties with Corinth (Thuc. 1.56.2), the Potidaeans appealed successfully to Corinth, resulting in the Athenian siege of the city (Thuc. 1.58–65). Soon afterward, the Corinthians, supported by the Megarians and the Aeginetans (Thuc. 1.67),21 put pressure on the Spartans to take action against the Athenians, and the Spartans issued an ultimatum, which the Athenians on Pericles’ advice rejected (Thuc. 1.145).
The outbreak of the Peloponnesian War occurred in the spring of 431, when the Thebans attempted to invade the recalcitrant Boeotian city of Plataea, a loyal ally of Athens. This act of aggression officially broke the terms of the Thirty Years’ Peace (Thuc. 2.7.1). Soon afterward, the Spartan King Archidamus led the Peloponnesian army into Attica, where he began the first of what was to be a series of annual invasions; hence the first phase of the Peloponnesian War is conventionally known as the Archidamian War (431–421). The Spartan strategy was to ravage Attic agricultural land in order to draw out the Athenians into a hoplite battle against the superior Peloponnesian land forces. Following Periclean strategy, however, the Athenians remained behind their walls, relying on their strong navy to import what they needed and to conduct reprisals on the Peloponnese by sea.22
In spite of the devastating plague that struck Athens in 430 (carrying off Pericles himself in the following year), at first the Athenian strategy was successful, culminating in the fortification in 425 of an outpost at Pylos in Messenia (ancestral homeland of the Spartan helots), which resulted in the shocking capture by the Athenian commanders Cleon and Demosthenes of 120 Spartan hoplites on the nearby island of Sphacteria.23 Overconfident as a result of this unexpected success, the Athenians (induced by Cleon) continued to reject Spartan negotiations for peace (Thuc. 4.41.3–4), and made a serious miscalculation the following year in engaging in a pitched hoplite battle at Delium in an attempt to democratize Boeotia and sway it away from the Peloponnesian side.24 The bloody defeat that the Boeotian army inflicted on the Athenian forces at Delium proved conclusively that the latter were no match on land.25 After the disaster at Delium, matters went rapidly downhill for the Athenians, when the Spartan