While there are several monarchies that date back over one thousand years, there is one throne that dates back over two thousand years. The Japanese monarchy, also known as the Chrysanthemum Throne, was officially founded in 440 BCE.
The Japanese monarchy is the oldest continuous hereditary monarchy in the world, and its official founding date is 11 February, 660 BCE.
While the monarchy claims mythological origins, the first recorded Emperor was Emperor Jimmu who reigned from 660 to 585 BCE. There have been 125 recorded Japanese emperors.
There have historically been eight Empresses of Japan that ruled in their own name. As of 1889 when the new Imperial Household Law was introduced, only males can sit on the Chrysanthemum Throne. This is known as agnatic primogeniture.
When female members of the Japanese Imperial Family marry, they lose their royal title if they choose to marry a commoner. Because there are so few aristocratic families left in Japan, most women in the Imperial Family do end up marrying commoners if they do marry.
The Japanese Imperial Family has been facing a succession crisis in the last decades. Because only male descendants of a male line can inherit the throne and there have been relatively few male children, there have been questions asked if the succession laws should be revised.