According to the Smithsonian, the earliest evidence of tattoos dates back to around 3,200 B.C. This evidence comes from the discovery of the "Iceman," a tattooed mummy found in 1991 near the Italian-Austrian border.
The tattoos found on the Iceman were composed of dots and small crosses on the lower spine and right knee and ankle joints. These areas correspond to areas of strain-induced deterioration, and the tattoo placement suggests that they were therapeutic and initially applied to ease joint pain.
The Smithsonian also describes evidence that the ancient Egyptians sported tattoos. In addition to finding several tattooed mummies, archaeologists have uncovered small bronze tools that seem like tattooing supplies.