Spartans did not feel comfortable with such a large Athenian force inside their city. If the Athenians were to turn their backs on Sparta, the city would not be able to protect itself. At this point, Sparta acknowledged that Athens might be getting too powerful. According to Thucydides, the Athenians were deeply offended by their removal from Ithome. They denounced their original treaty with Sparta made during the Greco-Persian Wars, then proceeded to make an alliance with Argos, a major enemy of the Spartans.  460—Athens' Clash with Corinth over Megara: Megarians joined the Delian League due to a war between Megara and Corinth. This angered the Corinthians. Even using Athens' weakest soldiers, being the old and young men who were left behind in the city, they were able to win the war against Corinth with ease.  460—The Athenian Expedition to Egypt: Athens led a coalition with the Egyptians to rebel against Persia. However, their six-year expedition did not lead to much success against Persia, as 100 Athenian ships were destroyed in the Delta region.  458—The Long Walls: The construction of the long walls gave Athens a major military advantage by forming a barrier around the city-state and its harbors, which allowed their ships to access waterways without threat from outside forces. Two walls were constructed from the city to the sea, one to Phaleron and the other to Piraeus. Athens relied on these long walls to protect itself from invasion, while sending off its superior vessels to bombard opponents' cities.  458—The Battle of Tanagra: According to Thucydides, Spartans aided the Dorians by invading Greece, because they were motivated by ethnic solidarity. Sparta sent out 1500 Hoplites and an additional 10,000 from their allies' forces to suppress the Phocians' Army invading Doris. The Spartans were victorious, but they found themselves stuck in this foreign land. Athens, suspecting a plot by the Spartans to overthrow the democracy and to prevent the building of the Long Walls, then attacked the Spartans at Tanagra in Boeotia with a force of 14,000. The Spartans were victorious in this battle.  457—The Battle of Oenophyta: After the Spartans returned home from Tanagra, the Athenians conquered Boetia and Phocis after a battle at Oenophyta. They then proceeded to tear down Tanagra's fortifications.  450—The Peace of Callias—Although this peace treaty is subject to scholarly debate, allegedly Athens and Persia agreed to a ceasefire.  447—Athens' forces were defeated at Coronea, causing the Athenian army to flee Boeotia.  446—The Peloponnesian Invasion of Attica: Athens continued their indirect war with Sparta by attempting to gain control of Delphi.