I think this is the wall of the Chapel of Santa Teresa and Tesoro Catedralicio.
This is the part of the Mosque added under involvement of Al-Hakam II (962-966),
or maybe even later by Al-Mansur (991-994), the 3rd and last enlargement.

Correction to these details are most welcomed. This site is so huge,
it is impossible to remember the details after all these years.