The Cerdà Plan is an urban development project designed by the Catalan engineer Ildefons Cerdà in the mid-19th century. It aimed to expand the city of Barcelona beyond its medieval walls, promoting a grid layout that allowed for better ventilation, light, and green spaces. The plan emphasized social equality by providing housing for various social classes. Cerdà's vision included wide streets, parks, and a mix of residential and commercial areas. Although not fully realized as intended, the Cerdà Plan significantly influenced the urban landscape of Barcelona, particularly in the Eixample district, which showcases its characteristic grid pattern and modernist architecture.