Book of Chess of Alfons X (13th cent.) [fol. 75v]
"This is the game that they call in Spain emperador (emperor), because he (= Alfons X. of Spain, declared Roman Emperor for some time) made it.
There is another game of tables that they call in Spain emperor because he made it and it is set up and played in this way. The one player should place his fifteen pieces on the one-point in one table. And the other [places] his fifteen pieces in the other [one-] point that is in the table next to it on the same side of the bar.
And he that should win the battle is to play first and bring his pieces by the rolls of the dice around through the tables of the board until he brings them into the table where the other had his [pieces]. And the other player should do this same thing towards him in the opposite direction.
And if in passing the ones should hit the others, they must return to the table where they first were placed. And from there they must be taken again as before until they come to the table where they should be set up. And in passing by each other and being hit and returning again as above in order to play he that bring them around to the table where he should and bears them off safely, he wins the game."
[from fol. 76r]
"This game they call medio emperador (half emperor)
There is another game that they call medio emperador and it has this name because just as the other game that we described above is played on the four tables of the board, so this one is played on two tables. And it is played with two or three dice but there is no prime like the other one but there can be a tie.
And because the game emperador is played on the whole board and this one only on half of it and with two dice, therefore they call it medio emperador.
And this is the explanation of this game."