English: The "Book of All Kingdoms" [f0fXX], of 1350, tells the voyages of an anonymous Castilian friar and is illustrated with 113 flag images, referred to (though seldom described) in the text.

The 2005 Spanish illustrated transcription of the "Book" [f0f05] shows for "Esclavonia" a vertically divided flag, red at hoist with a small, white eight-pointed star in the middle, and yellow at fly; the flag is shown in the ogival default shape of this source.

The anonymous author of the "Book" describes the flag thusly: E el rey d'esta Esclavonia á por señales un pendón amarillo a meitades, en la meitad bermeja que está cerca la vara está una estrella blanca, e la otra meitad del cabo es amarilla atal (And the king of Slavonia has for sign a yellow pendon in halves, on the red half which is near to the rod is a white star and the other half at the end is yellow like this).