371 BC

In 371 BC, on the plain of Leuctra, Spartans were defeated again from the Theban Sacred Band, this time under the leadership of General Epameinondas, though the Theban forces were outnumbered by the Lacedaemonians, Epameinondas with a series of ingenious tactics and with the help of his supreme trained men of the Sacred Band defeated the invincible Spartan army. He arrayed the best men of his troops, fifty shields deep, opposite to the opponent right wing occupied by the Spartans, which were twelve shields deep, leaving his center and left wing weak and ordering them to stay momentarily out of action.

The battle started with the engagement of Spartan and Theban cavalries, which ended quickly with the defeat of Spartans. Pelopidas leading the Sacred Band fell upon the Spartans with irresistible force but the Spartans fought bravely and at first were victorious. It was only when leading Spartans fell that the Spartan lines pushed and broke carrying away the rest of the army and driving them to the camp. King Kleombrotos of Sparta and many of his officers were killed. The rest of the army hardly had any serious fighting. From the 700 Spartans who took part in the battle, only 300 survived. The whole Hellas was in sock from the event, understanding that a new power had risen. At Argos, there was a revolution and the people put to death many of the upper class pro-spartan.

After the battle they sent heralds to Athens proclaiming their victory over the Spartans, but Athenians were not satisfied with the turn of events. Now they had a new superpower a few miles from Athens. They also sent a herald to Jason of Pherae in Thessaly. Jason upon hearing the news said he would come quickly in Thebes with triremes, but instead with great speed and passing through enemy territory he arrived in Boeotia. There the Theban leaders proposed him to attack the encamped Spartans and her allies. Jason and Epameinondas refused and managed to persuade them to let them go and thus saving Spartans from a bigger catastrophe. Spartans indeed soon left and at Aigosthena they met with Archidamos who was marching to help them. From there they returned home.

With the battle of Leuctra, the Hegemony of Greece passed from Sparta to Thebes, but for the short time of ten years. It did no good and as that of Sparta it hurt Greece greatly. Thebes had no experienced and knowledgeable men, nor her economy could withstand this. It failed as Sparta did, to unite the Greek cities and stop the blood bath of Greece. There was turmoil all over Peloponnese. The inhabitants of Mantinea in Arcadia, which had been broken in several villages, took back their capital and build new walls. In Tegea of Arcadia, the people formed an Arcadian federation. In two years time a powerful confederation was born that was including except the old alliances, Phokis, Locris, Aitolia and Euboea. After the battle of Leuctra, Thebes made again peace with Athens and wanted to destroy Orchomenos for being in alliance with the Spartans. The city was saved thanks to the great efforts of Epameinondas, but not for long. A few years later when Epameinondas was at an expedition in Byzantium, the city was razed, its male citizens were killed and the rest were sold in slavery. That, it was another big blunder by the Thebans.

Thebes invades Laconia

In Arcadia, an ally of Thebes, king Agesilaos of Sparta was ravaging its territories. In reply to this, Thebes sent an army under Epameinondas. When Agesilaos heard the news, he evacuated Arcadia and returned to Sparta, to protect her.
Upon Epameinondas arrival in Arcadia, he joined forces with members of the confederation from Arcadia, Argos and Elis. The total number of the army force was amounted to about fifty thousand men. The confederation pressed strongly Epameinondas, to invade Laconia, explaining to him that there was a general discontent and by this time many Perioikoi had revolted.

He was finally persuaded and in the autumn of 370 BC, invaded Laconia from four different routes, marching towards Sparta.
Only the Arcadians encountered serious resistance, by the Spartan Ischolaos at Ium, in the district Skiritis. Ischolaos and his divisions fell to the last man.

Finally, they all met at Sellasia, which they destroyed and burned and from there, they marched towards Sparta, which was saved from king Agesilaos, who had taken a series of defenses to protect the unwalled city.

Epameinondas who understood the danger of an attack towards the city in human loss, abandoned any further attempts to conquer the city. From there, burning and plundering villages, he marched towards the port and arsenal of Sparta, Gythium, which he attempted to conquer for three days, without success.

Epameinondas then returned to Arcadia and under his supervision a new city was built at the banks of the river Helisson, as the capital of the Arcadian confederation and it was named Megalopolis (the big city). In Megalopolis, a synod of deputies from all the towns of the confederation, was to meet periodically, to manage their affairs.
After this Epameinondas entered Messenia, in order to liberate her from the Spartans. In the mean time defection among the Perioikoi and Helots had already started. Epameinondas re founded Messene and in the hills of mount Ithome built excellent fortifications stretched for four miles, which are still preserved today. All of these had a devastating effect in the economy of Sparta, which lost half of its territory for ever and had no more the people to provide for its military.

In the meantime, Sparta had asked help from Athens. Iphicrates with an Athenian army of twenty thousand men, marched to Arcadia. Epameinondas hearing the news evacuated Laconia quickly and headed to Arcadia. The two armies, though close, did not engage in full battle. Iphicrates, who decided that his mission had been accomplished, returned to Athens.
Epameinondas too, returned to Thebes and he was put to a trial, because he extended the time of his expedition and also for being pacific and inactive. He defended himself successfully, increasing even more his popularity.
The accomplishments of his expedition were great. He weakened and humiliated Sparta and at the same time he increased the reputation of his army.

Because it was essential to communicate with her allies, in the spring of 369 BC, Epameinondas again tried to invade Peloponnese, but this time Athenians, Spartans and their allies were occupying the line of mount Onean and Kenchreae, in order to prevent him to enter Peloponnese. Epameinondas arrived and tried without success to make them fight in battle, even though his army was smaller. He encamped and a few hours before day break surprised them, by attacking and defeating the Spartan and Pellenian line. He was thus enabled to enter Peloponnese and join with his allies Arcadians, Elians and Argians. Sikyon deserted Sparta, after a vote taken by its people and admitted an harmost and a Theban garrison into its Acropolis. The same did Pellene. After the army ravaged the territories of Epidauros and Phleious, he tried by surprise to take the town of Corinth, but they defeated by the Athenian general Gavrias, who resisted with great skill. After this unsuccessful attempt, the Theban army returned home.

During the year of 368 BC, Epameinondas did not undertake any expedition into Peloponnese, instead Pelopidas with an army Theban force entered Thessaly, to protect Larissa from king Alexander of Macedonia. Pelopidas forced him to solicit peace, taking among the fifty hostages the future king of Macedonia, the son of Amyntas, Philip, who stayed for some years at the city of Thebes.

In 366 BC, Thebes enlarged the confederation by including cities of the Corinthian gulf and Achaia, but lost them again, when demanded that their oligarchic government ought to be deposed. That was a great mistake, showing the luck of experienced men.

In 364 BC, after insistence of Epameinondas, a large number of war ships were constructed and sailing them towards Hellispond. Epameinondas succeeded to win over Byzantium. Financial difficulties as well as luck of experience in maritime, put an end in the ambitions of Thebes.