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

Ancient Sparta’s government was a complex combination of monarchy, rule by a few, and rule by its people, which some scholars called a ‘mixed constitution’, and 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, but they did not rule alone.

Instead, the Gerousia, or Council of Elders, made up of 28 men over the age of 60 who were chosen for life, alongside the two kings, checked their authority. 

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

After reviewing those proposals, it made the final decision on major matters, acting as the democratic part of this system. 

In this way, kings, Gerousia, and Apella formed the core of the Spartan government, with them at its head.

Beyond these institutions, a further level of oversight was provided by the Ephors, a group of five officials chosen every year by the Apella. 

They held real influence because they served both as leaders and as a check on the kings’ power. 

If a king was thought to have gone beyond his authority, the Ephors could even put him on trial, illustrating how carefully power was balanced in this city-state. 

The dual kingship of Sparta goes back to myth and early traditions of the city-state. 

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 kings, and each brother went on to found a royal line: one the Agiad house and the other the Eurypontid house. 

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

Although this story is based on myth, it was very important in Spartan society and influenced its political system. 

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 concentrating in one person’s hands.

This system also allowed leadership to continue during war; 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 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. 

This military role was their most important duty, as history often shows when they led troops, such as by King Leonidas at the Battle of Thermopylae.

In addition, the kings had key religious duties. 

Those monarchs acted as chief priests of the state and performed various religious ceremonies and sacrifices. 

This mix of military and religious duties shows how connected these areas were in Spartan society. 

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

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

Although the Spartan dual kingship system had clear benefits, it also had problems and criticisms. 

These included power struggles between the two rulers and confusion and slow decision-making, which could weaken Spartan society. 

One of the clearest issues was the chance of conflict between the two kings. 

These arguments could cause political instability, slow decisions, and divide support among citizens and the army. 

The historical record shows several times when kings from the two royal families clashed. These clashes caused periods of tension and conflict in the state.

The diarchy could also slow down decisions. Since two kings had to agree on important matters, the system could stall, especially if the kings had different views. 

Some critics said that although the dual kingship kept one person from having all the power, it still kept power only with a few people. 

Because the kingship passed from parent to child, it stayed within the two royal families. This arrangement prevented more citizens from taking part in government. 

Also, the Ephors’ power to limit the kings sometimes led to struggles that could unsettle politics. 

The Ephors, chosen from the citizens, could remove a king, which sometimes led to direct conflict with the royal families. 

Over the centuries, some Spartan rulers 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.

To illustrate, 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 debated 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 wanted to make significant changes. Recognising 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, and by the time the Romans conquered Greece, the kings of Sparta had much less power. 

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 became a Roman provincial centre. 

Sparta’s unique political institutions, such as the dual kingship, were removed and replaced by Roman systems, although the city kept some local control.