With a strong Spartan army in Boeotia and the threat of treason in the air, the Athenians marched out with as many troops, both Athenian and allied, as they could muster to challenge the Peloponnesians. The two armies met at the Battle of Tanagra. Before the battle, the exiled Athenian politician Cimon, armoured for battle, approached the Athenian lines to offer his services, but was ordered to depart; before going, he ordered his friends to prove their loyalty through their bravery. This they did, but the Athenians were defeated in the battle, although both sides suffered heavy losses. The Spartans, rather than invading Attica, marched home across the isthmus, and Donald Kagan believes that at this point Cimon was recalled from exile and negotiated a four-month truce between the sides; other scholars believe no such truce was concluded, and place Cimon's return from exile at a later date. Athenian success can also be attributed to them making an alliance with Argos, Sparta's enemy and only threat for control over the Peloponnesian league. The alliance between Athens and Argos was moreover seen as a defensive measure to counteract Sparta's military strength.