Marseille marigraph, Tide gauge observatory in 7th arrondissement, Marseille, France.

The Marseille marigraph is a light beige stucco building with a terracotta hipped roof, set on a rounded bastion of pale interlocking stone blocks above the sea at Anse Calvo. Its facade has two dark-framed barred windows and a dark red door, with a short chimney on the roof. A black iron railing runs along the upper terrace, and a curved stone wall encloses a lower concrete platform with steps down to the water.

Constructed in 1883 and officially establishing France's zero altitude reference point on January 1, 1897, this scientific instrument has maintained nearly uninterrupted sea level measurements for over 140 years.

This classified historical monument represents Marseille's deep maritime heritage and serves as the fundamental reference point for altitude measurements across France and its overseas territories.

Located on the Corniche near Villa Valmer, the facility houses both original mechanical equipment and modern digital sensors that provide essential data for climate change research and coastal management.

The mechanical totaliser installed in 1885 is the only surviving example of its kind in the world. It is still maintained and calibrated every year, and weekly readings are taken alongside those of the digital gauge so that any apparent rise in sea level cannot be blamed on a change of instrument.