modifications made, which included alterations to improve the communication systems. Modifications were carried out in both buildings in the 1960s and were directed by Alejandro de la Sota. Antonio de Sala-Navarro and Reverter carried out further repairs and alterations between 1980 and 1992. The decline in the use of postal mail in the late twentieth century gradually reduced the functions of the complex, and, as a result, it began to lose its importance. In 1993 it was declared a Bien de Interés Cultural (Asset of Cultural Interest) and classified in the ‘monument’ category. At the beginning of the 21st century it was incorporated into the municipal estate and became a cultural centre and seat of the City Council of Madrid. History Madrid was growing in population and size in the seventeenth century after the decision of Philip II of Spain to transform the city onto an administrative and political centre for the nation. The Calle de Alcalá initially began at Puerta del Sol and ended at Paseo del Prado (at the height of the Plaza de Cibeles). Madrid's population growth meant that postal communication during the reign of Fernando VI of Spain was promoted through the construction of the Real Casa de Correos (Royal House of Letters), which was allocated to the Spanish architect Ventura Rodríguez. After the crowning of the new monarch Charles III of Spain, Charles III reassigned the architect Jamie Marquet to the city. The building served as the Casa de Correos (Post Office) until the construction of the new "Palacio de Comunicaciones". The location in the heart of the city resulted in road congestion and slow communication. The widening alterations to Puerta del Sol in 1856 led to the Casa de Correos finally hosting the Ministry of the Interior. The preliminary draft was approved by the minister of Public Works, Claudio Moyano, for the expansion on 19 July 1860; following the proposal project of the architect and engineer Carlos María de Castro to expand the old city limits. During Spain's restoration period, the Paseo del Prado and Recoletos continued being the preferred location for prestigious institutions and organisations, as well as mansions. Examples include, Buenavista Palace (the Army General Headquarters), which was designed by the architect Juan Pedro de Arnal in 1776 for the Dukes of Alba and the Palacio del Marqués de Linares (Palace of Linares), which is currently the Casa de América. One of