Roman conquest ramped up considerably at the end of the third century BC,
and as it moves towards the eastern Mediterranean, a clash with the Greek world became inevitable.
The Republic had to fight in Greece and Asia Minor for more than a century,
and one of the most significant conflicts was against the Seleucid Empire.
This war, known as the Syrian War, was concluded during the classic Battle of Magnesia.
Rome was founded in 753 BC in the Apennine Peninsula and was first ruled by kings,
only to transform into a republic in 509 BC.
Its initial expansion was slow, but by the third century BC most of the peninsula fell under its control.
By the middle of the century, the Republic faced its first big challenge in two bloody wars against Carthage.
Despite initial setbacks, Rome won both conflicts later known as the Punic Wars
and became the dominant force in the central and western Mediterranean.
As the Macedonian Kingdom had allied itself with Carthage,
Rome now had an excuse to intervene in the affairs of Greece.
However, another empire was rising in the East.
One of Alexander's heirs managed to found an empire called the Seleucid Empire after the man himself.
The Seleucid realm stretched from India to Anatolia and the Levant.
In 203 BC, the new Seleucid ruler Antiochus III entered an alliance with Philip V of Macedon.
But instead of helping him against the Romans during the Second Macedonian War,
he concentrated on conquering territories of the Ptolemaic Dynasty in Syria and Asia Minor.
After Rome defeated Philip V,
they declared a new policy titled "Freedom of the Greeks" and pulled out their forces
as they concluded that the eastern flank of their empire was now secured.
However, that left a power vacuum that Antiochus decided to exploit.
At the same time, Rome's greatest foe, the Carthaginian general Hannibal, joined the Seleucid court
and was pushing Antiochus to war.
The Aetolian League, which was allied with the Romans in the Macedonian War,
was not comfortable with the growing Latin influence in Greece
and were close to joining forces with the Seleucids.
The Romans used this tension as an excuse to station a few legions in Greece
and these legions quelled anti-Roman Sparta in 195 BC.
Antiochus continued instigating fear among the Greek city-states and in 192 BC, the Aetolian League
invited the Seleucid leader to Greece as a liberator.
Antiochus crossed the Hellespont and moved through Thessaly to besieged Larissa.
The Romans were aware of his movements
and used all their influence to prevent Macedon and the Achaean League from joining the Seleucids.
Their legions stationed in Greece, under the command of Appius Claudius, moved closer to Thessaly.
Antiochus was not aware of how weak the Roman forces in the area were
and when a small Roman force approached Larissa,
he panicked and retreated with his army to the island of Euboea where his forces spent the winter.
This proved to be a fatal mistake as the Romans used the pause
to move more than 20,000 of their troops from Brundusium to Apollonia in the spring of 191 BC.
Most of the Seleucid army was still in Asia, so Antiochus' position was very precarious.
He had just over 10 thousand under his command against 30 to 40 thousand Romans.
Instead of using his naval dominance in the Aegean Sea and retreating to Asia,
he decided to defend against the Roman legions at the legendary Thermopylae and wait for his reinforcements.
The passage of Thermopylae is long and narrow flanked on the sea by one side and swamps on the other.
Antiochus knew that there were two mountain paths that the Persians had used to outflank the Spartans
centuries before
and placed forces of his Aetolian allies to block these passages.
Roman general Manius Acilius Glabrio ordered two of his tribunes to attack these passages
and although one of the groups failed, the second overpowered the Aetolians.
Roman forces in front of the Thermopylae passage attacked head-on as that was the only way
but the Seleucid phalanx was able to stop the legionaries and pushed them back.
However, soon both forces saw that the Aetolians were retreating from one of the mountain passes.
They were being chased by the Roman flanking force.
That made the Seleucid phalanx retreat in panic,
but it was overrun by the Roman forces and almost all of Antiochus' forces were killed or taken prisoner.
The king himself fled at the first sign of trouble straight back to Euboea.
The defeat influenced the diplomatic situation.
The Aetolians sued for separate peace while Pergamon and Rhodes allied with Rome,
which created problems for the Seleucids' naval dominance.
This proved crucial as subsequent naval losses to the Rhodians in Eurymedon
and the allied Roman-Rhodian fleet took Myonessus,
completely negated the Seleucids' ability to attack Greece or Italy,
while the Romans and their allies now had the initiative to launch a counter-offensive.
The Romans pressed their advantage and their army led by Lucius Cornelius Scipio
crossed Macedonia and Thrace into Asia Minor in 190 BC.
Antiochus tried to negotiate but Roman demands were too high, so he had no other choice but to fight.
The king retreated slowly to the southeast and encamped in Magnesia,
near modern-day Manisa in Turkey.
Roman forces approached the Seleucid camp in the middle of December.
Roman historians claim that Antiochus had more than 70,000 troops, including 12,000 cavalry and 54 elephants
while the Romans and their allies from Pergamon, Macedon and Thrace amounted to 30,000.
This makes very little sense for the Romans
as nothing was forcing them to fight this battle against an army double their size,
and it is clear they were looking for this engagement.
Modern historians tend to think that the number of troops was similar
with both armies having around 50,000.
The battle took place on the 22nd of December, 190 BC to the northwest of the city of Magnesia
between the rivers Phrygios and Hermus.
The Seleucids had the Hermus to their left and the Phrygios to their right,
while the Romans and their allies had the Phrygios on their left flank and rear
and the Hermus on their right side.
The Roman center and left flank consisted of infantry
with just a few cavalry squadrons on their extreme left flank.
The infantry mostly consisted of Romans and their Italic allies
and they were formed in a traditional Triplex Acies with young hastati in front,
more experienced principes in the second line and veteran triarii as the final rank.
The right flank was manned by Rome's Hellenic allies and consisted of Greek peltasts and heavy cavalry.
The Romans also had 16 North African elephants
but their generals decided not to use them
as they were smaller and less aggressive than the Indian elephants of Antiochus.
The Seleucid center was built around 10 units of traditional Macedonian phalanx
and two more units of Galatian allies, with elephants between each of these groups.
Each of the flanks of Antiochus' army had 4,000 heavy cavalry,
among them cataphracts, with 16 elephants behind each group of cavalry.
Antiochus also had a group of chariots in front of his left flank
and groups of missile infantry on both of his wings.
Both armies had an unknown number of light missile troops in front of their heavy cavalry.
The battle started with Seleucid chariots attacking the Roman right flank.
This attack was greeted by a hail of slings, arrows and pila from missile units
and the chariots had to retreat in panic.
This panic spread to all of the left flank of Antiochus army
and when Roman heavy cavalry and allied peltasts attacked the Seleucid cataphracts,
the latter broke their formation and tried to escape, but they were killed to the last man.
The Romans did not have a great time on their left flank, though.
It was attacked by cavalry and light infantry led by Antiochus himself.
A small squadron of Roman cavalry was easily defeated
and the legion defending the flank had to retreat all the way to the camp.
Here the legionaries stopped their retreat and reformed their lines
as they received some reinforcements from the Macedonian allies defending the camp.
Although the camp itself was overrun by the Seleucid light infantry,
the legionaries held their position and stopped Antiochus' attack.
Unfortunately for the phalanx, it had lost cavalry support on both flanks and was soon surrounded.
Antiochus' attack on the Roman camp proved to be a mistake
as he wasn't able to protect his center from encirclement.
Although the warriors within the phalanx were disciplined and tried to retreat to the camp
they were soon overrun by attacks from infantry, cavalry and missile units.
The king's attempt to help his center came too late, as the Romans were already attacking the Seleucid camp
and so he fled all the way to Sardis.
The Seleucids lost the majority of their army while Roman losses were minimal.
Antiochus had to sue for peace.
A treaty was signed in 188 BC in the city of Apamea.
The Seleucids had to pay 15,000 golden talents and had to give away all of their holdings in Asia Minor.
The Taurus Mountains became the new frontier.
Former Seleucid lands were divided between Pergamum and Rhodes.
Antiochus and his descendants were also forbidden to fight any war in Europe or in the Aegean Sea,
while their navy was limited to ten large ships.
The Seleucids never returned to their former glory.
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