The Third Sacred War (355-346 BC) began as a dispute between Thebes and their neighbours in Phocis over the cultivation of sacred land, but expanded to include most of the Greek powers and was ended by the intervention of Philip II of Macedon, helping to confirm his status as a major power in Greece.
The war came at a time when Greece was in turmoil. The battle of Leuctra (371 BC) saw the Thebans inflict the first ever battlefield defeat on the main Spartan hoplite army (earlier defeats had been against small parts of that army). In the aftermath of that victory the Thebens, led in particular by Epaminondas and Pelopidas, had invaded the Peloponnese and liberated Messenia. This permanently reduced the power of Sparta by stripping her of many of the helots who had supported her army. The period of Theban dominance was short-lived. Pelopidas was killed in 364 BC, and Epaminondas was killed while winning another victory at Mantinea (362 BC). Thebes remained a significant military power, but without truly impressive leaders. Athens had slowly recovered from her defeat in the Great Peloponnesian War, and had founded a second Athenian League. At first this had helped boost her power and the League had been ruled with some moderation, but heavy handed Athenian rule eventually triggered a series of revolts (Social War, 357-355 BC), which ended with the loss of much of the league. To the north Philip II of Macedon had only recently come to the throne, and although he had overcome several threats to his power and probably greatly reformed the Macedonian army, was not yet seen as a major player.
The war was triggered by a religious dispute, although at its heart was a long standing rivalry between Phocis and Thebes. The citizens of Amphissa in Phocis were accused of cultivating the sacred plain of Crisa by the Boeotians. The Amphictyonic council, a religious council with responsibility for defending the Temple of Apollo at Delphi, found the Phocians guilty, and imposed a heavy fine. The same council meeting also condemned the Spartans for their actions before the recent Boeotian War, and both accusations were probably triggered by a Theban desire to secure their dominant position in Greece.
The Phocians responded by appointing a militant anti-Theban, Philomelus, as commander of their army. He managed to get financial support from King Archidamus of Sparta, and used it to hire a sizable mercenary army. He then used that army to capture Delphi (probably in 356), but at this point he left the treasuries at Delphi alone. Ambassadors were sent across Greece, and the Phocians gained support from Athens and Sparta. It is possible that the nearby Locrians, long-term rivals of the Phocians attempted to expel them from Delphi and suffered a defeat (probably near the cliffs of Phaedriades, on Mt. Parnassus, 355), a battle that is almost certainly recorded twice within a few paragraphs by Diodorus Siculus. At this stage Diodorus also records an invasion of Locris, in which Philomelus unsuccessfully attacked an unnamed fortress, lost twenty men in a battle, and then won a second battle triggered by the refusal of the Locrians to return the bodies of the dead from the first one.
In 355 Thebes convinced the Council to declare sacred war against Phocis. Thessaly, Locris and a number of smaller powers decided to support the Council, while Athens and Sparta were the main supporters of the Phocians. The threat of a large Theban led army (at a time when Thebes was the main military power in mainland Greece) forced Philomelus to raid the treasuries at the Sanctuary of Delphi, and use the money to raise a mercenary arming, paying one and a half times the normal wages. This gave the Phocians an effective army 10,000 strong.
In 354 the Phocians invaded Locris once again. They defeated a combined Locrian and Boeotian army in a cavalry battle at an unnamed location, and then defeated the Thessalians and their allies in battle at an otherwise unknown hill called Argolas, somewhere in Locris.
This run of success came to dramatic end later in the same year. The Boeotians, led by Thebes, raised 13,000 men, supported by another 1,500 Achaeans, from the northern coast of the Peloponnese. After a period of standoff, the two armies clashed in heavy woodland near the village of Neon. This time the outnumbered Phocians were defeated, and Philomelus threw himself off a cliff to avoid capture. Command of the army was taken over by Philomelus's brother Onomarchus, who managed to get the survivors back home.
By now the war had split Greece into two warring camps. Macedonia and Thessaly had sided with Thebes, while Athens and Sparta (led by King Archidamus III) supported Phocis.
The war came at the same time as the rise of Philip II of Macedonia. In 354 he captured Methone, on the slopes of Mt. Olympus. This alarmed the Athenian leader Demosthenes, but despite his best efforts he could rarely convince his fellow Greeks of the danger from the north.
Onomarchus appears to have been a more radical leader than his brother. He convinced the Phocians to continue with the war, and plundered the temple goods to increase the size of his army. He also used some of the money to bride the Thessalians into temporary neutrality. He then invaded Locris, where he captured the town of Thronium and forced Amphissa to submit. He then invaded Boeotia, where he captured Orchomenus, and besieged Chaeroneia.
Onomarchus and the Phocians were now a significant power in Greece. Lycophron, tyrant of Pherae (in Thessaly) asked for their help against Philip II, who was increasingly involved in the affairs of Thessaly. Onomarchus sent 7,000 men under his brother Phayllus into Thessaly, but he was defeated by Philip. This forced Onomarchus to move his main army into Thessaly. He then inflicted two battlefield defeats on Philip, including one where he may have lured Philip in an ambush and then used his siege engines against the Macedonians. Sadly neither of these battles are named in the survived sources. Philip returned to Macedon, while Onomarchus returned to Boeotia, defeated the Boeotians at Hermeum and captured Coroneia.
Onomarchus's run of success was ended by Philip, who returned to Thessaly to avenge his earlier defeat. Both sides brought sizable armies, with Onomarchus fielding 20,000 infantry and 500 cavalry. Philip's Thessalian cavalry outperformed the Phocians, and Philip was victorious (battle of the Crocus Field, c.353 BC). Onomarchus was killed while attempting to escape from the battlefield, along with thousands of his followers. After this victory Philip advanced south through Thessaly, and reached Thermopylae, the site of the famous Greek stand against Xerxes nearly a century and half earlier. Just as in that earlier war the Athenians and Spartans managed to act together and sent reinforcements to the Phocians. The allies blocked the pass, and Philip decided to withdraw.
Onomarchus was succeeded by his brother Phayllus. He was able to recruit fresh troops by offering higher pay. Phayllus also led his troops into Boeotia, but in his first campaign suffered defeats near Ochomenus, on the Cephisus River and near Coroneia. An expedition north into Epicnemidian Locris was more successful, although an attempt to capture the city of Naryx ended as a costly failure. He was then attacked by the Boeotians in his camp near Abae and suffered another defeat, which allowed the Boeotians to raid Phocis. They then attempted to lift a siege of the 'city of the Narycaeans', but were caught by surprise by Phayllus, who forced them to retreat and then captured and destroyed the city. Soon after this Phayllus died of an unnamed illness, and was succeeded by Onomarchus's son Phalaecus.
At first the young Phalaecus was supported by Mnaseas, one of Phayllus's officers. This arrangement would be short-lived, as Mnaseas was killed in a night battle with the Boeotians. Soon after this, Phalaecus was defeated in a cavalry battle near Chaeroneia. The Thebans were then distracted by a conflict in the Peloponnese. Phalaecus captured Chaeroneia but was then defeated by the returning Thebans, who were then able to raid into Phocis.
In 347 the Boeotians raided the border area of Phocis around Hya or Hyampolis. They were then defeated in a battle near Coroneia, and the Phocians were able to capture several Boeotian cities (Orchomenus, Coroneia and Corsiae are listed). The Boeotians then carried out another raid into Phocis, but were defeated on the way home. In the aftermath of these setbacks the Thebens asked Philip II for help. The Boeotians were still capable of winning victories on their own, including dispersing a Phocian forced that was building a fortress near their borders at Abae.
In the same year Phalaecus was accused to stealing from the remaining sacred treasures and was removed from his command. He was replaced with three generals - Deinocrates, Callias and Sophanes.
Our knowledge of this period of the war is probably distorted by the general hostility of the sources to the Phocians, who having lost the war were condemned for their sacrilege. Presumably they must have won some military victories, or the war wouldn't have lasted quite so long.
While this constant low level warfare was going on in Phocis and Boeotia Philip turned his attention east. He reached the Hellespont and the Chersonese, and entered into negotiations at Byzantium. This was a crucial area for Athens, controlling the trade routes into the Black Sea. He also signed an alliance with the King of the Odrysians in Thrace, removing a major threat to his eastern flanks.
Next Philip began to threaten Chalcidice, three peninsulas that jut out into the Thracian Sea and sat between Philip's original kingdom and his conquests in the east. The Chalcidians entered into an alliance with Athens, and over the next few years the Athenians sent three expeditions to help the defenders of the city of Olynthus, but they were unable to save it from Philip. The city surrendered in 348 and was razed to the ground. He destroyed a total of 33 Chalcidian cities and the area became part of Macedonia.
In 347 Philip received the Theban request for assistance against Phocis, but at first he only sent a handful of men. In 346 the Phocians requested help from the Spartans, who according to Diodorus sent 1,000 hoplites under the command of King Archidamus. They also recalled Phalaecus, who was restored as general. This proved to be something of a mistake. Philip was now ready to move south. He was also ready for a more general peace, and entered into peace negotiations. The Athenians sent an embassy to his court at Pella, led by Aeschines, Demosthenes and Philocrates. The ambassadors appear to have been rather overwhelmed by the court, and won over by Philip's charm. When the Macedonian ambassadors returned to Athens the assembly voted in favour of a peace treaty that acknowledged the status quo, in effect acknowledging Philip's conquest of Chalcidice and Amphipolis. Phocia was left out of the treaty, allowing Philip to continue the Sacred War if he so wished (Peace of Philocrates).
The Athenians then had to send an embassy to Pella to formally sign the treaty. In July 346 the two sides agreed to the Peace of Philocrates. Philip signed for Macedonia, Thebes and all of his allies, while Athens pointedly stood alone.
Philip brought his army south, and once again approached Thermopylae, where he had been forced to turn back earlier in the war. This time the pass was defended by Phalaecus, but he was no longer willing to fight, and instead negotiated with Philip. Philip agreed to let Phalaecus leave unhindered, and he took his mercenary force south into the Peloponnese (a force of 8,000-10,000 men). This left Phocis undefended, and the Phocians surrendered to Philip.
After the surrender Philip called a meeting of the Amphictyonic Council, and handed over the punishment of Phocis to the council (although presumably he played a major part in its decisions).
Phocis suffered a comparatively mild punishment (at least compared to some that were apparently suggested, including one suggestion that they should be thrown off a cliff, one punishment for temple robbers). The Phocians were expelled from the Amphictyonic Council, and were forbidden to use the shrine at Delphi. They were banned from owning horses of weapons, and their existing weapons were destroyed. Their cities were to be destroyed, and their population scattered into small villages of no more than fifty houses, each at least one stade from the next. Finally they were to pay back the money they had taken from Delphi during the war, at a rate of sixty talents per year.
Philip was rewarded with the two Council votes that had previously been held by the Phocians. He was also given the right to preside over the Pythian Games, on the grounds that both Phocis and Corinth, the normal hosts, had committed sacrilege. Philip also ended the war with control of Thermopylae, meaning that he had easy access to the heart of Greece from the territory of his Thessalian allies.
Philip would soon return to central Greece, after the outbreak of the Fourth Sacred War (339-338 BC). This time the war would be decided by a major battle, at Chaeronea (338 BC), in which Philip crushed a combined Theban and Athenian army, giving him effective control of almost all of Greece as head of the League of Corinth.