Diarchy in the context of "Leonidas I"

The fall of the Serbian Empire was a decades-long process in the late 14th century. Following the death of the childless Emperor Stefan Uroš V in 1371, the Serbian Empire was left without an heir and the magnates, velikaši, obtained the rule of its provinces and districts (in so-called feudal fragmentation), continuing their offices as independent with titles such as gospodin, and despot, given to them during the Empire. This period is known as the dissolution or the beginning of the fall of the Serbian Empire.

Between 1365 and 1371, King Vukašin was the co-ruler of Emperor Uroš, ruling the southern half, thus the Empire may be viewed as a de facto diarchy. Before 1371, the nobility were either directly subordinate to Emperor Uroš or to Vukašin. Vukašin died in the Battle of Maritsa (1371) against the invading Ottoman Empire, and southern Serbian provinces became nominal Ottoman vassals. Four months later, Uroš died. The lords could not agree on the rightful ruler; they dismissed Prince Marko, the son of Vukašin, and conflicts started between the nobles within a year. An assembly was held in 1374 without any success since the nobles were unable to agree on whether Marko or Prince Lazar would head the Serbian confederation as the Serbian king and the state continued as before, fragmented and without central authority.

Captains Regent (Italian: Capitani Reggenti; Romagnol: Capitèn Regìnt) are the two heads of state of the Republic of San Marino. They are elected every six months by the Grand and General Council, the country's legislative body. Normally the Captains Regent are chosen from parties in coalition and serve a six-month term. The investiture of the Captains Regent takes place on 1 April and 1 October every year. This tradition dates back at least to 1243.

The practice of dual heads of government (diarchy) is derived directly from the customs of the Roman Republic, equivalent to the consuls of ancient Rome, except the Captains Regent hold no executive power.

The Agiad dynasty (Ancient Greek: Ἀγιάδαι, Agiádai) was one of the two royal families of the ancient Greek city-state of Sparta. They ruled jointly along with the Eurypontid dynasty, possibly from the 8th century BC onwards, being the senior of the two houses. The hypothetical founder of the dynasty was Agis I, possibly the first king of Sparta at the end of the 10th century BC, who subsequently gave his name to the dynasty. The two lines, who maintained an enduring rivalry, were, according to tradition, respectively descended from the twins Eurysthenes and Procles, both descendants of Heracles. The most famous member of the Agiad dynasty was Leonidas I, known for his heroic death at the Battle of Thermopylae in 480 BC. The last Agiad king was Agesipolis III, deposed by the Eurypontid Lycurgus in 215 BC.

For most of its history, the ancient Greek city-state of Sparta in the Peloponnese was ruled by kings. Sparta was unusual among the Greek city-states in that it maintained its kingship past the Archaic age. It was even more unusual in that it had two kings simultaneously, who were called the archagetai, coming from two separate lines. According to tradition, the two lines, the Agiads (Ἀγιάδαι, Agiadai) and Eurypontids (Εὐρυποντίδαι, Eurypontidai), were respectively descended from the twins Eurysthenes and Procles, the descendants of Heracles, who supposedly conquered Sparta two generations after the Trojan War. The dynasties themselves, however, were named after the twins' grandsons, the kings Agis I and Eurypon, respectively. The Agiad line was regarded as being senior to the Eurypontid line.

Although there are lists of earlier purported kings of Sparta, there is little evidence for the existence of any before the mid-sixth century BC.

A coregency is the situation where a monarchical position (such as prince, princess, king, queen, emperor or empress), normally held by only a single person, is held by two or more. It is distinct from diarchies or duumvirates (such as Andorra, ancient Sparta and Rome), where monarchical power is permanently divided between two rulers; and also from regencies, where a person, who is not legally monarch themselves, exercises monarchical power on the behalf of reigning monarch who is absent or unable to rule (for example due to illness or young age).

The first minister and deputy first minister of Northern Ireland are the joint heads of government of Northern Ireland, leading the Northern Ireland Executive and with overall responsibility for the running of the Executive Office.

Despite the titles of the two offices, the two positions have the same governmental power, resulting in a diarchy; the deputy first minister is not subordinate to the first minister. Created under the terms of the 1998 Good Friday Agreement, both were initially nominated and appointed by members of the Northern Ireland Assembly on a joint ticket by a cross-community vote, under consociational principles. That process was changed following the 2006 St Andrews Agreement, such that the first minister now is nominated by the largest party overall, and the deputy first minister is nominated by the largest party from the next largest community block (understood to mean "Unionist", "Nationalist", or "Other").