The question of whether an arrow can penetrate the human skull is a matter of forensic and historical science. The answer is not a simple yes or no, but depends on a precise combination of factors. Penetration requires overcoming the natural structural defenses of the cranium, involving the target’s anatomy, the physics of the projectile’s impact, and the specific design of the arrowhead. Under certain conditions, the human skull is vulnerable to a well-delivered shot.
Anatomy and Vulnerability of the Human Skull
The skull is a complex structure designed for maximum protection, yet it possesses inherent weak points. It is composed of three distinct layers: a dense outer table, a spongy middle layer called the diploë, and a dense inner table that protects the brain. The diploë layer, with its porous structure, acts as a shock absorber, helping to dissipate impact energy across the surface.
The thickness of the skull’s bone varies significantly across different regions, directly affecting its resistance to penetration. The frontal bone (forehead) and the occipital bone (back of the head) are generally the thickest, measuring approximately 6 to 10 millimeters. Conversely, the temporal bones on the sides of the head, particularly the squama, are substantially thinner, sometimes measuring as little as 3 to 4 millimeters.
These thinner regions, especially the temporal bone, represent the most vulnerable points of the cranium. An impact delivered here requires significantly less force to achieve penetration compared to a strike on the thicker forehead. Therefore, successful arrow penetration often relies on exploiting the skull’s regional structural weaknesses rather than overwhelming its maximum strength.
The Physics Required for Penetration
Penetrating the dense bone of the skull is fundamentally a problem of energy transfer, specifically kinetic energy and the concentration of force. Kinetic energy is calculated based on an arrow’s mass and the square of its velocity. For a projectile to breach the skull, it must deliver a minimum of approximately 33 foot-pounds (ft-lbs) of kinetic energy upon impact.
Historical warbows, such as the English longbow, generated draw weights between 100 and 185 pounds, easily exceeding the 33 ft-lbs threshold. The higher draw weights of historical weapons were specifically engineered to overcome dense barriers like bone. High velocity is particularly valuable in this equation because it scales quadratically, making a small increase in speed far more effective for penetration than a small increase in arrow mass.
The angle of impact also dictates whether the arrow’s energy results in penetration or deflection. A strike that hits the skull perpendicularly, at a 90-degree angle, maximizes the transfer of kinetic energy into the bone. If the arrow strikes at a shallow or oblique angle, the rounded surface of the skull is likely to deflect the projectile, regardless of its power.
Arrowhead Design and Bone Piercing Capability
The final variable is the specific geometry of the arrowhead, which determines how kinetic energy is concentrated. Historically, archers employed two primary types: the broadhead and the bodkin point. The broadhead features wide, razor-sharp blades designed to cause massive tissue damage in soft targets. However, its wider surface area makes it less effective against dense materials, as the force is distributed across a larger area.
The bodkin point is engineered specifically to penetrate armor and bone. This arrowhead is characterized by its narrow, square-section spike, which concentrates the entire force onto a minimal surface area. This extreme pressure allows the bodkin to punch through hard barriers that would stop a broadhead.
Historical and forensic evidence confirms the effectiveness of the bodkin point against the cranium. Archaeological findings have documented instances of bodkin-style arrowheads embedded deep within human skulls. While a powerful bow is necessary, the narrow, armor-piercing geometry of the bodkin point is the primary mechanical feature that makes the penetration of a human skull possible.