The Invalides was founded by Louis XIV in 1670: pour que ceux qui ont librement exposé leur vie et prodigué leur sang pour la défense de la monarchie passent le reste de leurs jours dans la tranquillité... which means "for those who freely gave their lives and bloods to protect the monarchy, in order that they had a good time here..."
It was built on a vast land outside Paris, between faubourg Saint-Germain and the city of the Gros-Caillou. The architect was Liberal-Bruant, then replaced by Hardouin-Mansart in 1676. The first stone was laid down in 1671 and Robert de Cotte completed the building works in 1750. Just imagine! We had 17 courtyards, 16 kilometres of corridors... A true palace!
Soon, we had more than 4 000 residents: the peak was reached during the murderous wars of Louis XIV and Napoleon. Disabled persons used to work here: they made tapestry or calligraphy. Convalescents were cured in the Invalides courtyards, converted as gardens: sisters from Charité, nicknamed "Grey sisters" managed these infirmaries.
Oh, did you notice, outside? Cannons! They were taken from enemies: among them, 8 pieces whose belonged to Frederic I, king of Prussia, brought back in France by Napoleon in 1806. An imperial edict said those cannons had to thunder all the French armies' victories...