Birkenstock 128163 Madrid Eva NarrowThe Birkenstock Madrid is the oldest member of the family of models, making it a classic. Launched as a fitness sandal half a century ago, this simple single strap model has gone on to become a firm fashion favourite. Its function and design have largely remained unchanged. The special positioning of the strap gently trains the muscles in the feet and calves with each step; the toes grip reflexes trigger this effect. Modelled on the cork original,