This is the tower of the Castle of Oreja.
It can’t have long. Already in the eighteenth century a traveller wrote in his journal: “… any day now it will collapse.” The cracks in the walls are big enough to put your arm in. And after a good rain whole shoulders of the great gypsum cliffs come crashing down. One that fell some years ago shaved away the very ground in front of the tower, so that just left of the main door—watch your step as you look inside the tower!—there is a drop of two hundred feet.
Oreja is nothing special. There are more than a thousand ruined castles and fortresses in Spain. Many like Oreja are now out in the middle of nowhere because the roads they guarded are no longer used.
Oreja watches over a ford of the Tagus River. She has been guarding the ford for well over 2000 years. The Romans called her Aurelia. There must have been at least a watchtower on the cliffs in ancient times.
The present tower that is ready to fall is all that is left of a huge complex of defense works built by both Moors and Christians. There were fierce battles here and at the foot of the cliff, in the river valley. The Moors took the castle away from the Christians in 1113; and the Christians didn’t get it back until 1139. King Alfonso VII sieged Oreja with a huge army but still it took him more than nine months to force the Moorish defenders to surrender the castle. Afterwards he handed it over to the Knights of Santiago (St. James) to defend for him.
That’s one of the famous battles Oreja saw, and that one is fact. But there is another one that would make Oreja more famous if anyone could be sure it happened here. Both Livy and Polybius mention it. Somewhere on the Tagus about where Oreja is Hannibal defeated a big army of native Iberians—Olcades and Carpetani—before he started off with his troops and his elephants for Rome. He made the enemy army cross the river to come after him and then cut them down with his cavalry while they were swimming. “It was certainly here at the foot of the castle,” said a nineteenth century writer. “For years farmers have been finding in the fields and on the banks of the river old battle detritus, spearheads, clay sling pellets, even a Carthaginian helmet and an old sword.”
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Great Names in History 
Thanks for your detailed answer.
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You’re welcome. I only wish there were some source from classical times.
Man of Roma: I’m afraid the sources, though there are many, are not too good.
A writer named José Cornide in his Travels, 1789-1793, cites Juan Antonio Pozuelo y Espinoza, who wrote a history of Ocaña at the beginning of the eighteenth century (The castle still belongs to Ocaña). Pozuelo is the one who mentions the “bones, spurs, darts, and other instruments that are fished out of the Tagus from time to time”. He even mentions a sword with a jewel-incrusted scabbard that was sent to the archbishop of Toledo, who gave it to King Philip II.
Quite a few later writers simply state that Hannibal’s battle took place under the castle, though they give no sources, so one suspects they copy the tradition from each other: Díaz Ballesteros, El Conde de Cedillo, Jiménez de Gregorio. “The Carthaginian army, at the Ford of Oreja, fought that great battle against the allied forces of the Carpetanos, Olcades, and Vacceos that the historians speak of,” writes Cedillo.
Alvarez de Quindós devotes a whole chapter of his Descripción histórica de Aranjuez (1804) to Hannibal’s battle. He even claims that the local place-names Valdeguerra and Valdeguerrilla preserve the memory of his battle.
Yes, it would be interesting to know if that “somewhere on the Tagus” was at the foot of that castle. What was the name of that writer talking about farmers finding for years Carthaginian arms right on that spot?