The royal decree that founded Sanse Historical milestone · San Sebastián de los Reyes, Área Metropolitana, Madrid Image of San Sebastián de los Reyes, not of the place itself. The Catholic Monarchs recognised from Medina del Campo the new settlement that thirty-two households fled from the lordship of Alcobendas had raised beside a hermitage. In January 1493 they appointed its first mayors. 2 de mayo de 1492 Photo: Javier Paniagua (CC BY 3.0) What to see and do in San Sebastián de los Reyes