Architecture and urban heritage have been decisive in the modernization of the historical centre of Santiago de Chile. As early as the first half of the nineteenth century they added value to this area of the capital. Public authorities, with the support of regulations, identified valuable urban heritage, incorporating it into urban transformations. For various practical or historical reasons, buildings and public spaces were preserved and eventually reused, giving birth to a renewed idea of planning, which took advantage of this existing heritage. The incorporation of new typologies into the colonial urban fabric, together with the conservation of traditional buildings and public spaces, produced memorable places, both in the republican and modern city. They enriched the urban practices and the city landscapes, offering a valuable continuity with the colonial and republican past. The integration of old and new stimulated the emergence of an urbanism of quality. This article focuses on three specific moments of that peculiar modernization process: the consolidation of the original colonial grid (1818-1846), Vicuna Mackenna's Transformation Plan (1872-1875) and Santiago's first official Urbanization Plan (1939).