The Ruins of St. Paul's are the ruins of a 16th-century complex in Macau including what was originally St. Paul's College and the Church of St. Paul also known as "Mater Dei", a 17th-century Portuguese church dedicated to Saint Paul the Apostle. Today, the ruins are one of Macau's best known landmarks. They are often, but incorrectly, mentioned as a former cathedral, a status they never had. In 2005, they were officially listed as part of the Historic Centre of Macau, a UNESCO World Heritage Site.
Built from 1602 to 1640 by the Jesuits, the collegiate was one of the largest Catholic churches in Asia at the time, and the royalty of Europe vied with each other to bestow upon the temple the best gifts. With the decline in importance of Macau, which was overtaken as the main port for the Pearl River Delta by Hong Kong, the building's fortunes similarly ebbed, and it was destroyed by a fire during a typhoon on the 26 January 1835. The Fortaleza do Monte overlooks the ruin. In 2014 Italian historian Angelo Paratico put forward the idea that this facade is somehow connected with a sketch by Leonardo da Vinci kept at Gallerie dell'Accademia in Venice. This could have been due to Francesco Melzi showing the codex to Carlo Spinola s.j. in Milan or by the architect Giacomo della Porta who designed the facade of the Chiesa del Gesu' in Rome.