Rationalism was an Italian Architectural Style that spreaded during the raise of Fascism. Rationalism started with a 17th century ideology, Enlightenment, the period of reason.

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Rationalism Characteristics
The most importat characteristics of the movement are:
- Priority of urban planning on the architectural project;
- The need for an increasing number of houses to solve the housing problem;
- The rigorous rationality of forms;
- The systematic approach to industrial technology and standardization;
- The conception of architecture as a key determinant of social progress.

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Rationalism, the Most Important Architects
1. Adalberto Libera was one of the most important Italian Rationalist architects. He was considered the author of many key works designed under the Fascist regime. Some of his most famous works are: Casa Malaparte, Palazzo dei Congressi and the post offices in Rome.
Casa Malaparte is a red house with inverted pyramid stairs on the Gulf of Salerno. It is completely secluded from civilization, it is accessible just by foot or by boat.

The house was commissioned by the Italian artist, Curzio Malaparte whose eccentric character in the end led him to oversee the design process, creating serious arguments with Libera. Malaparte wanted the house to recall his own personal character and become a place for loneliness,contemplation and writing.
2. Giuseppe Terragni was an Italian architect who worked during the fascist regime and pioneered the Italian modern movement under the rubric of Rationalism. His most important project is the Casa del Fascio built in Como, begun in 1932 and finished in 1936.

Casa del Fascio was also called Palazzo Terragni, the structure is a perfectly regular prism whose height is half the base length. The building is a perfect cube. Terragni used few materials, all chosen with a symbolic intention as well as troubleshoot, of course, the practical aspects of the daily destination of the edifice.
Image source: https://it.paperblog.com/terragni-le-avanguardie-europee-e-la-sedia-lariana-3167224/

Palazzo Gualino is an office structure in Turin, projected in 1928–30 for the entrepreneur Riccardo Gualino by the architects Gino Levi-Montalcini and Giuseppe Pagano.
It is a famous mark of early Italian rationalist architecture. The design was inspired to simplification of lines and attention to functionality and technical requests. The building features a symmetrical facade and several rigourous elements in line with the style.
Image source: https://www.pinterest.it/OrdineArchTo/palazzo-per-uffici-gualino/
Info source: https://study.com/academy/lesson/rationalist-architecture.html