The obvious choice would be Notre Dame. Note that the parvis (place in front of the cathedral) is more recent (it used to be crowded with houses, which would be destroyed during the general transformation of the city in the 1860s), but the towers were the highest buildings in town and easy to see from any of the numerous surrounding hills (Montmartre, Butte aux Cailles...). Also, the view from the Left Bank would be more or less the same as now.