 The architects who most developed this style in Spain were Ricardo Velázquez Bosco and Alberto del Palacio, although glass for façades and iron for structures were used to some extent by other architects, such as Antonio Palacios, Enrique María Repullés y Vargas or Narciso Pascual y Colomer.A notable example is the Palacio de Cristal del Retiro in Madrid.When the city of Barcelona was allowed to expand beyond its historic limits in the late 19th century, the resulting Eixample district by Ildefons Cerdà became the site of a burst of architectural energy known as the Modernisme movement.