Going by the descriptions we have in historical literature, and the drawings of Ruy d‘Andrade of horses he has known in the early 20th Century, this is what the zebro may have looked like. This is a photograph of a Sorraia mare, with more stripes added

There are some differences of opinions regarding the meaning of the term "zebro" in Portuguese. Fact is that up until the Middle Ages, official documents differentiate between the zebro and other wild animals. The Portuguese author Arsénio Raposo Cordeiro ("The Lusitano Horse—Son of the Wind") wrote regarding this matter:

"The Sorraia horse is probably a surviver of the equine type which existed until recently in a wild state and which in the Middle Ages was called 'zebro'…"

Although some authors assume that the word 'zebro' refers to 'bull, cow, calf, or bullock', the Lisbon Charter of 1179 is clear on this matter; it distinguishes clearly between the hide of the bull, of the zebro, and of the deer, each costing half a maradevi (ancient Gothic coin used in Spain and Portugal). In the 13th, 14th, 15th and even in the 16th century, one still finds similar references to the zebro, then considered a distinct equine. 
Curiously enough, even today one still can find various places between the rivers Tagus and Guadiana named 'Vale de Zebro' (zebro valley), invariably referring to areas which had been wilder, or less inhabited. In the same region one can also find places called 'Vale de Eguas' (valley of mares), and 'Vale de Cavalos' (valley of horses), thus distinguishing between the wild horse, or zebro, and the domesticated horse, the Lusitano, its probable descendant.

As Ruy d'Andrade pointed out as early as 1926, the Portuguese first used the term 'zebra' in Africa, to define a wild animal of the horse family.

The fact that the Portuguese named the African wild horse species "zebra" is a really strong indication for "zebro" (or "zebra", various spellings did occur) to have been the Portuguese term for a wild horse. That the area which recently became a Sorraia Refuge is one known as Vale de Zebro since medieval times is actually the icing on the cake!

S. Lûcio de Azevedo's mentioned in "Épocas de Portugal Económico, Es boços de Histórica“ official prices for wild animals according to the hunting laws in the year 1253. It says there regarding their hides: „Of the hides of wild animals, the zevro's is the most precious; they cost 30 soldos, more than those of wild bulls, which cost 27 soldos." The hides of elk and deer were even cheaper. In a different paragraph the worth of a dead zevro is given as 50 soldos, 30 for the hide and 20 for the meat.

Ruy d’Andrade wrote that a man from Benavente in Portugal first named the African wild horse "zebras" during a trip through the Congo in 1578, and that in 1450, in the Portuguese town of Evora the price for a zevro was ruled to be two dineros, from which he drew the conclusion that wild horses lived in that region at least until 1450.
In search for the original meaning of the term zebro, whether it applies to a wild horse or some other wild animal, there has been a valuable contribution made by Jesús Alonso from Spain. It stood to reason that the "zebro's" habitat was not confined to Portugal, but spread over much of the Iberian Peninsula, but Jesús Alonso found evidence to that effect. Not only that, but what he found clearly shows that the term did indeed apply to a wild equid—obviously the animal that Ruy d'Andrade tried to rescue, and which he named "Sorraia horse"!

Jesús Alonso found in Spain the Spanish counterparts to the Portuguese field names "Vale de Zebro", etc. The Spanish term for the zebro was "cebro", "encebro", or "encebra", and was in use in Spain up to the XVI century.

"They were reported to be wild equids, 'rat'-colored, and had stripes on the back and legs," says Alonso. "So they were probably nothing but Sorraias.“ 

Some Spanish town and field names still bear the word Encebro, Cebro, or Encebra, such as Encebras (villages in Cuenca, Alicante and Granada), Cebreros (a village in Avila), or the Cebreiro (a mountain pass in Galicia)—and these are just a few examples.

Evidently, the equid zebro, encebro, or encebra has been mentioned by different Spanish sources from the XIV to the XVI century in an area covering at least South, Central and Eastern Spain (that is where encebro-related field names are found). Jesús Alonso found historical sources that mention the encebro, such as the book "El Libro de La Montería" (meaning "The Book of Hunting"), written in the first half of the XIV century under the auspices of king Alfonso XI of Castile. This book describes, often tediously, the best places for hunting within the domains of this king. It concentrates mainly on bear and boar, but says in one of the chapters about the medieval wildlife of Cartagena (in Murcia, southeastern Spain) that "encebras" lived there.

Besides in the El Libro de la Montería, encebras are mentioned in other sources: The "Relación de Chinchilla", written in 1576, describes the animals living around Chinchilla in southeastern Spain and describes the encebras as "ash-colored mares", resp. colored like rats, „a bit short, whinnying like mares, and running faster than the best (riding) horse".

"Colored like rats" is indicating clearly that they were grullas, as the Portuguese term for grullas is "rato", which means "mouse" or "rat". This also strongly indicates that the original color of the Sorraia (or zebra, or encebra) was grulla (mouse-dun/rato), and not dun (baio). 


This Sorraia has good leg stripes, better than most do nowadays. Is the gradual disappearing of the stripes due to the severe inbreeding?


 The "Arte Cisoria", written by a Valencian called E. de Villena, mentions encebra meat and says that it was eaten as a remedy against idleness/lazyness (back then, people often thought that by eating the flesh of an animal, that animal's energy, vitality, strength and abilities would become their own).

In the medieval tale "Romance del Rey Marsin" one of the verses says, "There goes King Marsin, a knight riding on a zebra, for lack of a (riding) horse".

The Libro de la Montería mentions encebras in the mountain areas of Murcia in book III, page 192, saying:

"The Villa Franca river is a good range for boar and enzebras in winter." "Cabezas de Copares is a good place for boar and enzebras in winter." "The Sierra de Zelchite is a good place for boar in winter and there are plenty of enzebras."

Here is another text found and translated by Jesús Alonso:

"Zebro is the name given in the middle ages, in Portugal, León and Castile, to a certain species of wild equine that lived in some parts of the Iberian peninsula until it became extinct towards the end of the XV century. In the kingdom of Aragon it was better known as Zebra or Encebra.

Medieval chronicles describe the zebro as a domestic ass-like animal, but taller, stronger and sturdier, besides being very fast and ill-tempered. The coat was greyish ("rat coat" is the term commonly used in medieval descriptions), interrupted by a black stripe along the back. It seems the nose was also black, and it had stripes on the legs. They lived in herds that preferred to wander on the plains, but withdrew to the mountain regions due to hunting and pressure from domestic stock.“

Around the end of the XV century and the beginning of the XVI century, the zebro disappears from the hunting chronicles, probably due to its extinction. However, there are isolated mentionings in later writings. 

The zebro's identity has been debated for a long time. At first it was thought they were simply feral asses of the North African species Equus asinus atlanticus, introduced a bit before the Roman conquest. But several aspects did not fit: their wild and unruly behaviour, their greater size and the fact that they were whinnying like horses. The possibility that it was an endemic species of the Iberian Peninsula grew stronger and stronger.

The last area where the zebro was abundant in Spain, the southeast, kept some field names regarding this animal, such as Valdencebro (Teruel), Encebras (Alicante), or Las Encebras (Murcia), and Ribeira de Zebro in the municipality of Moura, Portugal. 

Fernando Prado from Brazil mentioned that a book titled "800 Years of Hunting in Portugal" describes the zebro as a hemionus (halfass). However, there are several reasons why that is unlikely:

1) Perhaps the strongest indication for the zebro to have been a horse, not a hemionus, is that the zebro is reported to have been whinnying like horses—no hemionus subspecies does that.

2) Zebros are described as having had dark, or black, noses—which would be consistent with rato color, but not with the mealy mouth found in wild asses and halfasses.

3) None of the hemionus species have prominent leg stripes. Although they usually do have a dorsal stripe, and the Onager has a really broad one, their legs are light in color, mostly nearly white, as are their bellies and flanks. The Somali wild ass—not a half-ass—does have leg stripes, in contrast to the Nubian, but even it doesn't have an appearance like the striped horses Ruy d'Andrade knew and portrayed, likely to remind the Portuguese explorer around Africa of their native wild equines when seeing zebras there... Especially the Quagga must have come pretty close in appearance to dun-factor horses as Ruy d'Andrade portrayed and desrcibed them. None of the wild asses and halfasses really resemble the zebra in color.

4) All hemionus species, and subspecies, are of a yellowish or reddish color, set off with whitish areas—Onager, Kiang, Khur, Kulan, Dschiggetai, and the Syrian hemionus. None of them are what one could call rato (grulla). Of course one couldn't rule out the existence of a rato-colored hemionus subspecies in southwestern Europe, namely, Iberia, but that is really a far stretch; all existing hemionus are in color more like a light baio than rato.

5) Archeologists and paleozoologists are agreed on the existence of a hemionus in Europe (and a wild asinus population as well) in prehistoric times, but say it became extinct about 7,000 years ago at the latest. All hemionus species and subspecies are and were found in Asia and Arabia—far from Iberia. Again, it is some stretch, and cries for substantiation, to claim that they should have become extict everywhere else in northern Africa and the Mediterranean, but survived in Iberia—the farthest from their original stronghold.

The size of the zebro also speaks rather against a hemionus, as it is reported to have been larger.

Maybe something that one should also consider here is Ruy d'Andrade‘s report of his first encounter with the wild bunch of horses that inspired him to pursue his Sorraia project: He wrote that he was reminded by them of a hemionus herd. It can't be ruled out that people less educated in equines than he was would simply have considered them to be a different kind of animal (species), which they called zebro/encebro—they wouldn‘t have thought them to be half-asses, because they wouldn‘t have known about such animals, but they must have looked sufficiently different from what they were used to as riding and work horses. Today, the breeding in captivity lets Sorraias become more and more small editions of the modern Lusitano, but there used to be those that were quite different in phenotype—leaner, with less muscling, rafter-hipped, often ewe-necked, and with longish ears. Such horses, especially when in poor condition, definitely resemble a hemionus to a degree.

Jesús Alonso said: "I do not think zebros were wild asses, not only because of the whinnying or the color, but also because wild donkies were not mentioned by Greeks or Romans, who, on the other hand, mentioned the existence of wild horses."