The walls of Mansilla de las Mulas, the greatest example of medieval fortification in the province of León date back to the 12th century, the period, in which Fernando II repopulated the town. Every forty metres there were watchtowers that connected the walls, now disappeared. Remains of the fortification include large fragments of the wall and several battlement towers.
The Church of St Eustace was built between 1532-1632. St Eustace"s is considered a masterpiece of late Gothic architecture. The church’s reputation was strong enough of the time for it to be chosen as the location for a young Louis XIV to receive communion. Mozart also chose the sanctuary as the location for his mother’s funeral. Among those baptised here as children were Richelieu, Jeanne-Antoinette Poisson, future Madame de Pompadour and Molière, who was also married here in the 17th century. The last rites for Anne of Austria, Turenne and Mirabeau were pronounced within its walls. Marie de Gournay is buried there.
The origins of Saint Eustache date back to 13th century. The church became a parish church in 1223, thanks to a man named Jean Alais who achieved this by taxing the baskets of fish sold nearby, as granted by King Philip Augustus. To thank such divine generosity, Alais constructed a chapel dedicated to Sainte-Agnès, a Roman martyr.