I've been reading a book about Suleiman the Magnificent, and in his ride to Istanbul, four units are described as guarding him. I know the Spahis are sort of the land owning cavalry corps similar to Knights of Europe and all, and the slave soldier shock troops of the Janissaries, and the rivalry between the two. However, two are described that I've never heard of. My google searches only get me the quote from Ogier Ghiselin himself, but describes the other two as cavalry units called "Ghourebas" and "Ouloufedjis", of which I've never heard of, in any military histories or even games such as AoE and Total War.
What are they, what was their social role and standing, and where they in any famous battles or engagements of any sort, or were they a ceremonial unit of some sort simply meant to Guard Suleiman on the way to Istanbul? Thanks in advance.
Okay, so there are two kinds of sipahi, the timarlı sipahi and kapıkulu sipahi. The timarlı are the land-owning cavalry everyone knows, and the kapıkulu are the elite cavalry. They are under the direct command of the sultan just like the janissaries, and their members are mostly made up from devşirme graduates or former janissaries (though this will change later as the devşirme began to be abandoned). The kapıkulu was also known as the altı bölük halkı (people of six regiments), which comprised of one silahtar regiment, one sipah regiment, two ulufeci regiments, and two gureba regiments. The sipah is the most prestigious regiment, followed by the silahtar, the ulufeci, and the gureba.
The ulufeci means salaried men, and they're pretty much the same as the sipah and silahtar. The gureba is a bit different as they're intended to be filled with military personnel and volunteers who routinely displayed extreme bravery and valor in combat. However, there doesn't seem to have been a strict distinction for the sourcing between regiments. They all moved with the sultan or the commander in chief and positioned themselves around him in battle so most battles involving the main army will always contain the kapıkulu cavalry. Regiments of the kapıkulu also often gets assignment outside of battle, and for the gureba it was usually reinforcing raiding mission done by the akinci
For further reading A Military History of The Ottomans by Mesut Uyar is the best book on the general Ottoman military i know