The boundary-line between arrondissements XIII and XIV is Rue de la Santé, the name of the great Paris prison which stands there. It brings us to the vicinity of the Paris Observatory and of the Hôpital Cochin. The prison is a modern structure on a site known as la Charbonnerie, because of coal-mines once there. The Observatory, built over ancient quarries, was founded by Louis XIV’s minister Colbert, in 1667. A spiral staircase of six hundred steps leads down to the cellars that erewhile were mines. It was enlarged in 1730 and again in 1810, and the cupolas were added at a later date. A stretch of Rue du Faubourg St-Jacques borders its eastern side, and there on the opposite side we see l’Hôpital Cochin, founded in 1780 by the then vicar of St-Jacques-du-Haut-Pas, whose name it bears--enlarged in recent years. At No. 34 of Rue du Faubourg St-Jacques we turn into the seventeenth-century Rue Cassini, so named in 1790 to memorize the seventeenth-century organizer of the Observatory. Here Balzac lived in 1829 in a house no longer standing. The great painter J. P. Laurens has an _hôtel_ here. We find a Louis XVI monument in a court at No. 10. Subterranean passages, made and used in a past age by smugglers, have been discovered beneath the pavement of this old street. Rue Denfert-Rochereau has its first numbers in arrondissement V. This was the “Via Infera,” the Lower Road of the Romans. The name _Enfer_, given later, is said to refer, not to the place of torment, but to the hellish noise persistently made in a _hôtel_ there built by a son of Hugues Capet, the hôtel Vauvert, hence the French expression, “envoyer les gens au diable vert”--_vert_ shortened from _Vauvert_, i.e. send them off--far away--to the devil! _Enfer_ became _d’Enfert_, to which in 1878 was added the name of the general who defended Belfort in 1870: not exactly a happy combination! Many persons of note have dwelt in this old street. No. 25 (arrondissement V) is an ancient Carmelite convent, built, tradition says, on the site of a pagan temple: an oratory-chapel dedicated to St. Michael covered part of the site in early Christian days and a public cemetery. An ancient crypt still exists. It was in the convent here that Louise de la Vallière came to work till her death, in 1710. That first convent and church were razed in 1797. The Carmelites built a smaller one on the ancient grounds in 1802, and rebuilt their chapel in 1899. It did not serve them long. They were banished from France in 1901. The chapel, crypt and some vestiges of the ancient convent are before us here. Modern streets--Rue Val de Grâce opened in 1881, Rue Nicole in 1864--run where the rest of the vast convent walls once rose. No. 57 is on the site of an ancient Roman burial-ground of which important traces were found in 1896. No. 68, ancient convent of the Visitation. No. 72 built in 1650 as an Oratorian convent, a maternity hospital under the Empire, now a children’s hospice. No. 71,