Archbishop Jean-Baptiste Lamy had brought in two French architects, Antoine Mouly and his son Projectus, to work on the St. Francis Cathedral project, and suggested that the Sisters could make use of their services on the side to build a much-needed chapel for the academy.

[4] Projectus ended up being the main architect for the project, basing his Gothic Revival design—complete with spires, buttresses, and stained glass windows imported from France via the Santa Fe Trail—on the famous Sainte-Chapelle in Paris.

[citation needed] Loretto Chapel is best known for its helix-shaped staircase (nicknamed "Miraculous Stair"), which rises 20 feet (6.1 m) to the choir loft while making two full turns, all without the support of a newel or central pole.

[4] By this point, the chapel was substantially complete but still lacking access to the choir loft, possibly due to the unexpected death of the architect, Projectus Mouly, in 1879.

[12] According to the version of events passed down by the Sisters of Loretto, multiple builders were consulted but were not able to find a workable solution due to the confined quarters.

[7] The staircase as originally built lacked handrails and was reportedly so frightening to descend that some of the nuns and students did so on their hands and knees.

In the early 2000s, amateur historian Mary Jean Cook theorized the probable builder of the staircase as François-Jean "Frank" or "Frenchy" Rochas (1843–1894), a reclusive rancher and occasional carpenter who came to New Mexico from France around the 1870s.

Cook also found an entry in the Sisters' logbook stating that Rochas had been paid US$150 (equivalent to $4,736 in 2023) for "wood" in 1881, confirming that he had done some type of carpentry work for them.

At the time of his death, Rochas reportedly owned an extensive set of carpentry tools including:[7][15] five saws, a saw clamp and set, nine planes, nineteen moulding planes, two squares, five gauges, six chisels, two gouges, a draw knife, a brace, three augers, ten auger bits, a reamer, two clamps, and a pair of trammel points (for drawing large circles)Others have disputed Cook's theory.

Further afield, another staircase is in the Gdańsk Town Hall in Poland, which was reported to the New Mexican in 1944 by a government official named Bonnie Foster.

Afterward, the previously all-male St. Michael's High School turned co-ed in order to accommodate the Academy's female students.

[citation needed] The story was the subject of the 1998 television film The Staircase, starring Barbara Hershey and William Petersen.

In flashbacks, protagonist Dr. Neil de Hoyos recalls visiting the chapel and marveling at the staircase as a child in Santa Fe.