The film is loosely based on the life of the 11th-century Castilian knight and warlord Rodrigo Díaz de Vivar, called "El Cid" (from the Arabic al-sidi, meaning "The Lord").

To strengthen cordial ties to the Spanish government ruled by Francisco Franco, Bronston began developing a biographical film of El Cid.

The emirs return to Spain with orders to resume hostilities with the Christians while Ben Yusuf readies his army for a full-scale invasion.

Don Rodrigo Díaz de Vivar, on the way to his wedding with Doña Chimene, rescues a Spanish town from an invading Moorish army.

More interested in peace than in wreaking vengeance, Rodrigo escorts his prisoners to Vivar and releases them on the condition that they never again attack lands belonging to King Ferdinand of Castile.

To weaken his Spanish opponents he hires Dolfos, a warrior formerly trusted by Ferdinand, to assassinate Sancho and throw suspicion for the crime on Alfonso, who becomes the sole king.

Years later, Rodrigo, now known widely as "El Cid", is called back into the service of the king to protect Castile from Yusuf's North African army.

The ensuing battle goes well for the defenders until El Cid is struck in the chest by an arrow and has to return to the city in plain sight of the Moorish army.

Unwilling to abandon his army at this critical moment, Rodrigo obtains a promise from Chimene to leave the arrow and let him ride back into battle, dying or dead.

Guided by King Alfonso and Emir al-Mu'tamin riding on either side, the horse leads a mounted charge against Ben Yusuf's now terrified soldiers, who believe that El Cid has risen from the dead.

In the panic that ensues, Ben Yusuf is thrown from his horse and is crushed beneath Babieca's hooves, leaving his scattered army to be annihilated.

[6] The country of Spain was recommended to him as a filming location by Jose Maria Areilza, then-Spanish Ambassador to the United States when they were seated together at a dinner party in Washington, D.C.[7] Bronston agreed and established his namesake production studio near Las Rozas in Madrid.

[15] However, principal photography was nearly delayed when Cesáreo González's Aspa Films filed an infringement claim against Bronston over the project's thematic similarities.

[16] Previously, in July 1956, it was reported that two biopics of El Cid were in development: an American-Spanish co-production with Anthony Quinn set to star, and a collaboration between RKO, Milton Sperling, and Marvin Gosch.

[20] With filming set to begin, Barzman received a copy of the seventeenth-century play Le Cid by Pierre Corneille from the library of the French embassy in Madrid and used it as the basis for a new screenplay.

[10] Writing in his autobiography, in the summer of 1960, Heston had received Frank's draft which he described as not "good, ranging from minimally OK to crappy", but he was intrigued with the role.

[29] As he conducted research into his role, Heston read El Cantar de mio Cid and arranged a meeting with historian Ramón Menéndez Pidal.

[33] Orson Welles was initially approached to play Ben Yusuf, but he insisted that a double do his on-set performance while he would dub in his lines during post-production.

Prior to filming, Heston and British actor Christopher Rhodes trained for a month in the use in weaponry under stunt coordinator Enzo Musumeci Greco.

[50][48] Costume designers Veniero Colasanti and John Moore oversaw a staff of 400 wardrobe seamstresses which spent roughly $500,000 on manufacturing medieval-style clothing at a local supply company, Casa Cornejo, near Madrid.

The most expensive costume piece was a black-and-gold velvet robe worn by King Alfonso VI during the film, which was tailored in Florence, Italy from materials specially woven in Venice.

The Garrido Brothers factory, located in Toledo, Spain, worked under an exclusive contract for eight months producing 7,000 swords, scimitars, and lances.

Anthony Luna, a Madrid prop manufacturer, crafted 40,000 arrows, 5,780 shields, 1,253 medieval harnesses, 800 maces and daggers, 650 suits of mail (woven from hemp and coated with a metal varnish), and 500 saddles.

The collector's edition DVD also included a reproduction of the premiere's souvenir program and a comic book, as well as six color production stills.

[58] Bosley Crowther of The New York Times wrote "it is hard to remember a picture--not excluding Henry V, Ivanhoe, Helen of Troy and, naturally, Ben-Hur--in which scenery and regal rites and warfare have been so magnificently assembled and photographed as they are in this dazzler ...

The pure graphic structure of the pictures, the imposing arrangement of the scenes, the dynamic flow of the action against strong backgrounds, all photographed with the 70mm color camera and projected on the Super-Technirama screen, give a grandeur and eloquence to this production that are worth seeing for themselves".

[59] Variety praised the film as "a fast-action color-rich, corpse-strewn, battle picture...The Spanish scenery is magnificent, the costumes are vivid, the chain mail and Toledo steel gear impressive.

"[61] Harrison's Reports praised the performances from Heston and Loren and summarized the film as "raw and strong, brooding and challenging, romantic and powerfully dramatic.

"[63] A review in Newsweek described the film as being "crammed with jousts and battles, and its sound track is reminiscent of Idlewild airport on a busy day, but the dramatics in it explode with all the force of a panful of popcorn."

[67] Richard Corliss, reviewing for Time, wrote that "Like the best action films, El Cid is both turbulent and intelligent, with characters who analyze their passions as they eloquently articulate them.