Paris is like an onion, say the locals, it has many layers. And I would add, the more you peel, the sweeter it gets. The city is laid out in a circular spiral, that is sometimes caricatured as a snail or "escargot." This layout lends itself to the historical development of the city. It started originally on Île St.-Louis, the small island just next to Île de la Cité where the Cathédrale Notre-Dame de Paris has stood for over 800 years. It then kept expanding to encompass what is today the Left Bank neighborhood of the Latin Quarter and the Right Bank neighborhood of Le Marais, two of the oldest, and richest, historically speaking, neighborhoods of Paris. Over the centuries it expanded ever outward to encompass the 20 arrondissements that make up Paris today.
But historical is a relative word. When Left Bank sites like the Musée de Cluny house the Roman era baths, Les Thermes de Lutèce, that date back some 2000 years, then structures like the Eiffel Tower, being just a bit more than 125 years old, can seem relatively modern in this town.
One of the genius strokes of Napoléon was to engage urban designers who were responsible not just for the wide avenues, including the Champs-Elysées, but also for many of the luscious, large parks and gardens that give Paris its greenspace allure. One that pre-dates that era however is the Jardin des Tuileries created by André Le Nôtre in 1664.