Ptolemaeus is a huge crater with a circular formation, located a little south and a little west of the center of the lunar disk.
Alphonsus is located just south of Ptolemaeus, its north wall touching the south wall of Ptolemaeus. Its inner floor was impacted by the American moon probe Ranger 9, on March 24, 1965.
Arzachel is located just south of Alphonsus and is third in size in the set of three craters that form a north-south alignment (Ptolemaeus, Alphonsus and Arzachel). Arzachel is the deepest crater in this set. Its floor is flat and the walls that surround it are a notorious and classic example of a step-like formation or level curves (terraces).