The Theban campaign of 377 BC was the second attempt by King Agesilaus II of Sparta to force Thebes to accept Spartan control, but like his first attempt in the previous year the campaign ended in failure.
In 382 the Spartans had seized control of Thebes, but in 379 a combination of Theban exiles and internal enemies of the new regime overthrew the pro-Spartan government and expelled the Spartan garrison of the Cadmea (the citadel of Thebes), triggering the Theban-Spartan or Boeotian War (379-371 BC). The Spartans sent an army late in the year, but without success. In 378 King Agesilaus II led a second invasion of Theban territory. After forcing his way past some extensive field fortifications, he ran into a combined Theban and Athenian army three miles from Thebes, and was unwilling to risk attacking them in their strong position on a ridge. Agesilaus retreated back to Thespiae, where he restored the fortifications, before leading most of his army back out of Boeotia. A Spartan garrison was left at Thespiae, but later in the year that force suffered an embarrassing defeat at the hands of the Thebans, in which the Spartan commander Pheobidas was killed. After this setback the Spartans sent a fresh regiment commanded by one of their polemarchs to take over at Thespiae.
Agesilaus took command of the army that invaded Boeotia in 377. His first move was to order the new commander at Thespiae to secure the passes over the Cithaeron range. In an attempt to mislead the Thebans he then ordered the market for his army to gather at Thespiae. The Thebans, who had been preparing to defend a position at Scolus, south of Thebes, were fooled, and moved their army west onto the road from Thespiae to Thebes. In the meantime Agesilaus marched up the Scolus road, and was able to get past the previous Theban position without a fight.
This meant that Agesilaus was now in a dangerous position, between Thebes and the main Theban army. He advanced north-east across Boeotia, devastating the country as he went. The Spartans reached as far as Tanagra, a Spartan ally to the north-east of Thebes, before turning back. In the meantime the Theban army had rushed back from Thespiae, and took up a strong position on a hill called the 'seat of Rhea'. Agesilaus needed to find a way to dislodge the Thebans, and decided to carry out a feint west towards Thebes itself. The Thebans were forced to abandon their strong position and dash back towards the undefended city. They had the advantage of higher ground on most of this route, but were harassed by the Sciritae, Spartan hill men with an excellent reputation as scouts and elite troops. The Sciritae chased the Thebans all the way back to the city, before withdrawing. The Thebans put up a victory trophy, but this was more of a publicity gesture than a celebration of a real success.
The Spartans withdrew to the seat of Rhea, where they passed through the Theban field fortifications constructed in the previous year, and from there returned to Thespiae. They were harassed on their way by Theban and Athenian peltasts, but these attacks were eventually beaten off by Olynthian cavalry, Spartan allies since their defeat in the Olynthian- Spartan War of 382-379. After reaching Thespiae Agesilaus led most of his army back to the Peloponnese. On the way home he ruptured a vein in his leg while climbing an acropolis, and was thus unfit for the campaign of 376.
Although the Spartans hadn't posed a direct threat to Thebes during the 377 campaign, they had inflicted heavy damage on the Theban farmland, and food was now running short. The Thebans arranged to purchase supplies from Thessaly, and sent a convoy of transport ships escorted by two triremes to collect the grain. This meant that they needed to pass Oreus, on the northern coast of Euboea. This was one of the few places on the island still in Spartan hands, and the local harmost, Alcetas, was able to man three triremes. In order to trick the Thebans he got his three crews to exercise in one ship, and so the eventual attack, carried out on the return journey, came as a surprise. The entire convoy was captured, and the 300 crewmen were imprisoned in the citadel at Oreus. While Alcetas was in the city, possibly visiting a boyfriend, the Thebans broke out of their prison, seized the citadel, and inspired a revolt in the city. The grain and ships were recovered, and the crucial supplies reached Thebes. As a result the Spartan attempt to starve the Thebans into surrender failed.
The Spartan campaign of 376 was even less successful. This time Cleombrotus was in command, but after suffering a minor defeat in the passes across Cithaeron, he cancelled the invasion and returned home.