The walled complex of León is formed by the Roman wall, whose origin dates back to the 1st century, by the medieval fences or walls, from the 14th century, and by the castle of León, today the seat of the provincial historical archive. The walls were built by Legio VI to control the Asturian population in the area and rebuilt by Legio VII in stone in 74 AD. The first major reform was carried out in the Tetrarchic period, still under Roman rule.

The repopulation of the city in the 9th century by the Kingdom of Asturias led to the repair of the walls using the methods of the time. The first extension, on land, to the south of the city was carried out due to the increase in settlements outside the city walls, something that would eventually lead Alfonso XI to order the construction of fences to protect the new town.

The Castle Gate or Prison Arch, named after its location next to the castle of León, corresponds to the northern gate of the original Roman camp. The first recorded action was when Alfonso V, according to Madoz, repaired the four Roman gates, including the north gate, which had been destroyed by the Muslims. In any case, the physiognomy of this gate is not documented until the 18th century, although in 1757 the state of the gate must have been ruinous as work was commissioned to carry out the necessary repairs, including the Santa Ana gate. This work should not have been started, given that a year later the Town Hall stated that the Castillo and Moneda gates were in the worst state of repair instead of Santa Ana, and so work was begun and completed in 1759, the final result of which is what has been preserved to this day.

The case of the Castillo gate is unusual, because at that time the cities far from the border in Spain did not pay attention to the state of their defensive systems, so a new gate, annexed to the Roman wall and in Baroque style, must have been due to compelling reasons, although it is suspected that the main one was the imminent danger of collapse and ruin of the pre-existing one. If it was not demolished simply to create a new street, it is because León, having maintained its urban structure and remaining circumscribed to the space within the walls, maintained the function of its walls to enclose and control the population. The monumentality of the gate is justified by the trend of the time, in which the walls also served to embellish the city, so the effort was made to provide a monumental access to the city.

The gate is crowned by Don Pelayo, who at the time was considered the first king of León and reconqueror of the city from the Muslims. For a long time it was thought that it was not Pelayo, but San Pelayo who crowned the gate, but the restoration of the inscription plaque cleared up the doubts.

On 27 July 2008, part of the wall of León and an adjoining wall collapsed. The collapse took place in Calle Ruiz de Salazar, in the area corresponding to the final section of the wall in this street, at the corner with Calle Pilotos Regueral. The crumbling filled not only the area next to the wall with rubble, but the whole street, which is usually pedestrianised, although circulation is limited to residents and authorised vehicles. Today the wall is in a state of consolidated ruin, and is periodically restored. The City Council of León is its owner, and the construction is destined to be one more element in the tourist offer of the city. On 27 April 2005, the mayor of the city requested 150,000 euros from the Ministry of Culture for new restoration work, which has begun and continues in 2009.