Chapultepec Castle was really a former palace that had been converted into a military college in 1841.  According to Englishman John Phillips:

". . .The palace was erected by the Spanish Viceroy, Galvez, on a porphyritic hill which rises abruptly from the plain, at about two and one quarter miles from the city of Mexico.  Its situation is most commanding, and the view from it magnificent, as besides the city, the eye sweeps over an extensive plain, a considerable portion of which is cultivated. . .The view represents Chapultepec on the left, and diverging from it, an aqueduct of 900 arches, which supplies the city with water.  The city itself appears in the center of the picture, and on the right are the volcanic mountains of Iztaccihuatl and Popocatepetl."

Phillips view must have been taken before the war, or at least before the Mexicans fortified the castle in anticipation of the American advance on Mexico City.  Noticeably absent are the parapets, timber screens and other fortifications as well as the militgary college's round tower, known as El Caballero Alto.