Erythrocytes, also known as red blood cells, are synthesized in the bone marrow.

Specifically, they are produced in the red bone marrow, which is found in the spongy bone tissue of certain bones, such as:

* Flat bones: Skull, ribs, sternum, and pelvis

* Long bones: Ends of long bones like the femur and humerus

The process of erythrocyte synthesis is called erythropoiesis.