The femur is the thigh bone in the human body. In humans, it is the longest, hardest and strongest bone. The femur is said to be harder than concrete. The average human femur in adults is 48 centimeters (19 in) in length and 2.34 cm (0.92 in) in diameter and managed to support and withstand up to 30 times the weight of an adult. It forms part of the hip (at the acetabulum) and part of the knee. The word femur is Latin for thigh.

It is impressive that evolution could make the femur bone almost harder than concrete. It has probably taken millions of years of evolution for the femur to evolve into the super strong bone that is today. The femur is a critical building block that the rest of our relatively soft body relies on.