Do you like having a Queen? Perhaps not. Perhaps, though, you like it so much, you think it would be a good idea to have two ruling over you at the same time.
That might seem like a bizarre idea, but in the Greek city state of Sparta they had two kings as their heads of government.
Like our monarchy, succession was hereditary. You may feel that this a recipe for disaster as the two kings battled for power. There was some competition but, for the most part, they co-operated. Stability was helped by the fact that their areas of responsibility were split: one king was the commander-in-chief for the armed forces, and the other king took charge of domestic affairs.
This arrangement was particularly handy in violent times as, if one king was killed, there was already another in place to carry on as leader. Perhaps this is why King Leonidas thought he wasn't being too reckless when he faced a vast Persian army, at the Battle of Thermopylae (480 BCE), with a small Spartan force of only 300!
The Romans had quite a different view on monarchy. In the 5th century BCE they were ruled by Tarquininus Superbus. Trouble started when the king's son raped a woman called Lucretia who then, sadly, went on to commit suicide. A nobleman called Lucius Junius Brutus was so angered by this that he forcibly exiled the royal family.
From that time onwards, the idea of one man ruling through hereditary power was feared and hated. Rules were created to ensure it would never happen again. There were to be two ruling officers, Consuls, who were elected for one year only, with no immediate chance of re-election. In this way they limited the degree of power that any one man could gain.