 The westernmost of these two islands, the Île de la Cité, is Paris' heart and origin.Its western end has held a palace since even Roman times, and its eastern end since the same has been consecrated to religion, especially after the construction in the 10th century of the cathedral predecessor to today's Notre-Dame.The land between the two was, until the 1850s, largely residential and commercial, but since has been filled by the city's Prefecture de Police, Palais de Justice, Hôtel-Dieu hospital and Tribunal de Commerce.