Among the works of the so-called “transitional” military architecture from the last quarter of the fifteenth century, one of the most unique cases erected in the Iberian Peninsula is the Cubete of Carmona (Seville). This bastion built in the times of the Catholic Monarchs follows the new poliorcetic standards, but with forms, which are quite innovative and could be considered breakthrough. Conceived as a bastion external to the Alcázar Real, it has a moat in part connected with the moat of the main fortress. The bastion is open in the rear, and could be consider a ravelin, although its location is in an angle of the outer enclosure of the Alcazar, which preludes the subsequent pentagonal bastions. Its anomalous plan is a horseshoe shape that has been discussed by various authors, but so far, there has never been a fully detailed survey with elevations and sections, nor, above all, an attempt to address their hypothetical reconstruction. This paper presents new plans, sections, elevations and images that proves this work is unusual and truly revolutionary for its time.