The heart of the city is the ''Baixa'' or city centre; the Pombaline Baixa is an elegant district, primarily constructed after the 1755 Lisbon earthquake, taking its name from its benefactor, Sebastião José de Carvalho e Melo, 1st Marquis of Pombal, who was the minister of Joseph I of Portugal (1750–1777) and a key figure during the Portuguese Enlightenment. Following the 1755 disaster, Pombal took the lead in rebuilding Lisbon, imposing strict conditions and guidelines on the construction of the city, and transforming the organic street plan that characterised the district before the earthquake into its current grid pattern. As a result, the Pombaline Baixa is one of the first examples of earthquake-resistant construction. Architectural models were tested by having troops march around them to simulate an earthquake. Notable features of Pombaline structures include the ''Pombaline cage'', a symmetrical wood-lattice framework aimed at distributing earthquake forces, and inter-terrace walls that were built higher than roof timbers to inhibit the spread of fires.