How did the painted column in Andrea Mantegna's St. Christopher scenes add to the illusion of space?

In the scenes from the life of St. Christopher located in the Ovetari Chapel, Andrea Mantegna utilized a highly realistic, meticulously detailed painted column on the front plane to enhance spatial illusion.1

By placing this column on the front plane, Mantegna effectively divided the composition into two distinct scenes while creating the impression that the column existed in a realm separate from the pictorial space—a realm shared directly with the observer. This technique extended illusionistic principles to the elements surrounding the picture, bridging the gap between the painted narrative and the viewer's own physical space. This approach anticipated his later work on the San Zeno altarpiece, where he further integrated frame architecture with painted elements to conjoin the sphere of the artwork with the beholder's environment.12