The ancient Persians had an almost obsession with the number " one thousand “, And as such their regiments were divided into a thousand men known as hazarabam ( hazara indicating thousands).
The decimal system was also confirmed when ten regiments of this type were united to form a Division ( baivarabam ) of 10,000 men .
The so-called “ Immortals ”Or Amrtaka (in ancient Persian) formed the Baivarabam Division of the Persian king, and their "immortality" derived from their constant number - which was always held at 10,000 (according to Herodotus ).
In other words, the victims of this elite division were quickly replaced by the best candidates of other baivarabam Persians.
Like Herodotus continue to describe these Athanatoi (immortals) in the battle of Thermopylae (480 BC) :
… A group of Persians chosen under the leadership of Hydarnes, the son of Hydarnes. This body was known as the Immortals, because it was always held in power; if a man was killed or fell ill, the vacancy he left was immediately filled, so that the total body strength was never less - and never more - than ten thousand.
Of all the troops in the Persian army, the native Persians were not only the best but also the most magnificently equipped; I have already mentioned their dress and their armor, but I should add that each man shone with the gold he wore on his person in unlimited quantities. They were also accompanied by covered wagons filled with women and servants, all elaborately set up. The special food, separated from that of the rest of the army, was brought for them on dromedaries and mules.
The Greek historian also mentions their rich clothing (from the Persian army 560-330 BC)
The dress of these troops consisted of the tiara, or soft felt cap, embroidered tunic with sleeves, a mail coat that resembled the scales of a fish and trousers; for their arms they carried light wicker shields, quivers, short spears, powerful bows with reed arrows and short swords that swayed from the belts at the side of the right thigh.
As can be understood from such accounts, the Persian Immortals were probably very different from the strangely "dark" way they were depicted in the movie 300.
In fact, such elite divisions tended to flaunt their vibrant uniforms and armaments and refined - as is evident from their accounts of carrying spears with golden pomegranates, silver pomegranates and even golden apples. The latter mentioned the spears carried by the king's bodyguard unit of 1,000 men - known as Arstibara, but nicknamed "Melaia".