once, it's a matter of "eyes down" rather than "up" in
order spot the plaques and bollards that mark the levelling of Paris.
date from the 1850s when the level of a certain number of reference
points was established; these were later used as the basis for the
sewerage network (roughly 600 km under the Second Empire i.e. more
than 30km a year !) in which the water flows in accordance with
gravity and thus has no lowest point. The average sea level in France
is that of the Mediterranean which has barely discernible tides.
markers also indicate that the annexation of the villages between the
city wall ("Des Fermiers Généraux" 1789) and the
fortifications (Thiers 1840) was already outlined in the planned
sewerage system because some of them ran alongside main roads (the
red RN on road maps) and were thus outside Paris at that time.
they are hard to make out under successive layers of paint and
neglect by the City of Paris (they are too cheap to restore !). There
is an odd one out at avenue President Kennedy which is
embossed "general levelling" whereas the others have "Paris
levelling operations later took place throughout France by
Bourdalou (1860 - 1862) and Lallemand (1884 - 1922) the latter
being 7cm. lower than the former. Bordalou markers are especially
hard to spot in central Paris even if there are many of them. There is no link with the altitude
marker at rue du Télégraph which merely indicates a