Why was ancient Sparta always ruled by two kings at the same time?

According to legend, the dual kingship began with twin sons of Aristodemus, who was a descendant of Heracles (known as Hercules in Roman stories). 

When Aristodemus died, his sons, Eurysthenes and Procles, were still very young. 

Rather than choose one, the Spartan people made them both kings, and each brother went on to found their own royal lines: one the Agiad house and the other the Eurypontid house. 

From that moment, these two families ruled at the same time and started Sparta’s diarchy.

Although this story is based on myth, it was very important to Spartan society. 

When the Spartans linked their kings to Heracles, they gave their two-kings system a sense of divine approval and right. 

From a practical angle, the institution of two kings may have developed to stop power from being concentrating in one person’s hands.

This system also allowed leadership to continue during war time; while one king led soldiers into battle, the other could stay in Sparta to govern. 

Historians believe that having two kings also matched the political realities of the time. 

Sparta was not originally a single city but began as four separate villages, so establishing two royal families may have been an effective way to unify these groups under one government while still honouring local leadership. 

Having two kings might seem likely to cause conflicts, but in Sparta, their roles and tasks were clearly defined, which appears to have helped keep the system stable. 

The Spartan kings, even though they had high rank, did not have total power. 

As generals during war, they led the Spartan armies on campaigns, which was considered to be their most important duty.

As history often shows, they spent much of their time leading troops, such as King Leonidas at the Battle of Thermopylae.

In addition, the kings had key religious duties. They acted as chief priests of the state and performed various ceremonies and sacrifices. 

This mix of military and religious duties shows that the people believed that success in war depended on the gods’ support. 

In civil matters and legal cases, those rulers had limited power: they could speak in public, suggest new laws, and take part in some legal decisions.

In principle, the two rulers shared power equally, but in practice, the balance often varied, depending on each king’s personality, their relationship, and the wider political situation. 

Although those rulers had many social advantages, other parts of government controlled their power, especially the Ephors and the Gerousia.

Ancient Sparta’s government was a complex combination of monarchy and elements of what we would call 'democracy'.

As such, it included rule by a few, and rule by its people, which some scholars called a ‘mixed constitution’.

At the centre of this structure were two kings, each from one royal family: the Agiads and the Eurypontids. 

Their rule lasted their entire lives, and their main tasks were military and religious, so they led armies into battle and conducted religious ceremonies.

Rather than holding aboslute power, these two kings had to share it with other parts of Spartan government.

This includes the Gerousia, or Council of Elders, made up of 28 men over the age of 60 who were elected for life. 

The Gerousia prepared proposals for the Apella, or Assembly, which consisted of all male Spartans aged 30 and over. 

After reviewing those proposals, the Apella made the final decision on major matters, which was kind of like a democratic part of their system. 

In this way, kings, Gerousia, and Apella formed the most powerful core of the Spartan government.

However, it was the Ephors, a group of five officials chosen every year by the Apella, who held real influence over the kings’ power. 

If a king was thought to have gone beyond his authority, the Ephors had the power to put him on trial.

This was seen as an important way to balanced power in this city-state. 

Over the centuries, some Spartan kings made a clear impact on their city-state and on the rest of Greece by navigating the challenges of dual kingship in both war and peace.

Here are a few well-known examples:

Leonidas I (reigned from 490-480 BC)

Leonidas, from the Agiad family, is likely the most famous Spartan king because of his role at the Battle of Thermopylae during the Persian Wars. In 480 BC, he led a small Greek force that included 300 Spartans in a brave but doomed stand against a much larger Persian army under Xerxes I. His heroic death and the sacrifice of his soldiers became a symbol of courage and resistance against overwhelming odds. Although he died at Thermopylae, his actions brought Greek city-states together and helped them win against Persia. 

Agesilaus II (reigned from 399-360 BC)

A Eurypontid king, Agesilaus II, was one of Sparta’s most well-known and complicated leaders. Although he was lame from birth, an almost impossible obstacle in Spartan society, he became one of Sparta’s best military commanders. During this period, his reign took place as power shifted after the Persian Wars. He helped Sparta win battles during the Corinthian War, and following those victories, pushed for expansion by leading several campaigns in Asia Minor against the Persian Empire.

Cleomenes III (reigned from 235-222 BC)

From the Agiad family, Cleomenes III was an ambitious king who recognised that Sparta was losing power in Greece. He started a wide-ranging programme of social and political reforms to restore Sparta’s military and political strength. Although he did not succeed, his reforms showed he was willing to challenge old customs and institutions. 

The dual kingship system in Sparta lasted for many centuries. However, the political situation in the ancient world changed. 

Sparta’s decline began in the 4th century BC after its defeat at the Battle of Leuctra in 371 BC by the Thebans.

This loss ended its military control in Greece. In the following centuries, even though it tried several political and social reforms, it could not regain its previous strength. 

Its influence slowly faded, and by the time Rome conquered Greece in 146 BC, it was a poor shadow of its former self.

Following this, the Romans reorganised the Peloponnese into the province of Achaea, and the city of Sparta became just another Roman provincial centre. 

Sparta’s unique political institutions, such as the dual kingship, were removed and replaced by Roman systems.