The observatory was sponsored by King D. Pedro V and built in the Real Tapada of Ajuda using the similar scientific infrastructure built in St. Petersburg, Russia as reference. The Astronomical Observatory of Ajuda was one the most important of its kind at the time. Its construction began in 1861 and it became operational six years later. All its original observational instruments have been kept functional, making this a unique case in the world. In 1919, the observatory took part in a historical experiment, which involved multiple teams of scientists observing an eclipse (in São Tomé and Príncipe and in Brasil) to assess the validity of Einstein’s theory of relativity.