The cell division stage where chromosomes line up in the middle of the cell is called metaphase.

Here's why:

* Meta means "middle" in Greek.

* During metaphase, the chromosomes, which have already duplicated, are attached to spindle fibers, which are made of microtubules.

* The spindle fibers pull the chromosomes towards the center of the cell, aligning them along the metaphase plate, an imaginary line that runs through the center of the cell.

This alignment is crucial because it ensures that each daughter cell receives an equal number of chromosomes during the next stage, anaphase.