Meridians are the imaginary vessels for Qi, also known as life-force. They were widely believed to exist by Chinese people prior to the widespread scientific study of anatomy. At the time in China, the causes of disease were largely unknown, and dissection of the human body was a cultural and religious taboo until it was legalised in November 1913.
Blocked meridians were believed to cause disease, and it was thought that by inserting needles at points along the meridians, one could correct the blockage and restore normal flow of Qi, thus restoring health. This has long been disproven since the causes of disease have been proven to be bacteria, viruses, parasites, poisons, injuries, immune-disorders, DNA damage, congenital defects, and similar physical problems unrelated to the nonexistent meridians.