even wage war on each other. However, in 378 a League decision forbade internal wars if the League was operating an army outside of the Peloponnese, but perhaps this disposition had already been in place from much earlier and was a part of the constitution of the League. L. H. Jefery summarises the constitution of the League as "a circle centred on Sparta, with the spokes of a wheel but not necessarily with the added cross-links of a web." The League treaties contained defensive obligations: Sparta had to assist an ally attacked by a non-League member, and conversely the allies had to help Sparta in case of an attack. The famous Spartan fear of the helots is shown by a special clause providing that allies had to assist Sparta in case of a slave-revolt and must not offer citizenship to Messenians, because the Arcadians assisted the latter during the Spartan conquest of Messenia. This clause was activated in the 460s during the Third Messenian War. The treaties between Sparta and the allies were also permanent, with a clause forbidding secession. Several secessions did occur, but as a result of a breach of a treaty. Seceding members usually pointed out a breach of the treaties from Sparta to leave. The procedure to admit new members is not known. Sparta could either decide alone, or request the approval from their allies in the subsequent League congress. Another reason for the allies to remain within the League, despite their loss of autonomy, was the support of oligarchy by Sparta. The oligarchs that ruled most of the League members could rely on Sparta to retain their status in their city. Moreover, many of them had friendship ties with Spartan citizens, or even the kings. The Spartan king Agesilaus II (r.c.400–c.360) was especially known for his guest-friendships (xenia) among his allies. Thanks to these friendships, leading oligarchs could send their sons to the agoge, the Spartan education system, where they became trophimoi xenoi, and further developed their attachment to Sparta. Reform of 506 BC A major change in the organisation of the League took place c.506, when the Spartan king Cleomenes I attempted to capture Athens and place at its head his friend Isagoras as tyrant or as member of an oligarchy. A full army of the League was called and marched on Athens, but the Corinthians returned home when they discovered the purpose of