In Parshat Shoftim, Dvarim 17:14-16 we learn about the rules for having a king:

When you enter the land that the LORD your God is giving you, and have taken possession of it and settled in it, should you say, “I will set a king over me, like all the surrounding nations,” set over you a king whom the LORD your God chooses. The king you set over you must be one of your own people. You may not set a foreigner over you, who is not your brother. Further, he must not acquire many horses for himself; he must not make the people return to Egypt to acquire more horses, since the LORD has told you: You must not go back that way again.

Horses in Biblical times........

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