Another of these important palaces or suburban villas was seated on the northern slopes of the Butte Montmartre, which rises some hundred mètres above the level of the Seine, on the other side of the river,--a site which gave it an admirable extended view over the city and the surrounding plains. The most important ruins which have been discovered north of the river are the remnants of the aqueduct to convey water from Passy, large basins on the site of the Palais-Royal, various highways branching off to the north and east and extensive cemeteries near these roads, and numerous Roman medals and coins in various localities,--sufficient to demonstrate the existence of an extensive and important population. Montmartre is supposed to have derived its name from having been the site of a temple of Mars (_Mons Martis_); or from having been the scene of the martyrdom of Saint Denis, the first bishop of Paris, and his companions, A.D. 270 (_Mons Martyrum_). Buried under the modern pavement of the Ile de la Cité, the Gaulish _Oppidum_, are many vestiges of the Roman occupation. In 1847 numerous remains of the construction of houses during this period and of what was considered to be a church dedicated to the Virgin were discovered under the open place in front of Notre-Dame; of these, careful drawings were made, engraved, and published in the _Statistique monumentale de Paris_ and the structures then covered up again; in the following year, excavations made in the course of enlarging the Palais de Justice brought to light in the court of the Sainte-Chapelle and under the houses to the south of it remains of walls of the ancient Roman palace. The old historians of Paris, indeed, relying upon the testimony of Ammianus Marcellinus, state that one of the two Roman palaces was situated in the western end of the island which formed the ancient Lutetia. In 1844 the laying out of a new street between the Palais de Justice and the Hôtel-Dieu revealed two portions of edifices the use of which was unknown, but which, by the thickness of their walls and the nature of their construction, were supposed to have formed some part of the public structures. It has been considered that these various vestiges of important buildings situated in the centre of Lutetia indicate that they surrounded an open market-place or commercial exchange.