What technology was needed before capillaries could be discovered?

Before capillaries could be discovered, advancements in microscopy were crucial. The invention of the microscope in the 17th century, particularly with improvements by scientists like Antonie van Leeuwenhoek, allowed for the visualization of tiny structures in biological specimens. Additionally, techniques for preparing and staining tissues helped reveal the intricate networks of capillaries, enabling researchers to observe these small blood vessels for the first time.