Alicante, 150 Years Marking the Zero Level in Spain

Just 30 years had passed since the execution of the Martyrs of Liberty and a little over a decade since the first Spanish submarine, Narciso Monturiol's Ictíneo, conducted its official tests in the Port of Alicante, when the city was chosen to mark the zero altitude level in Spain. A milestone that this Monday marks its 150th anniversary since the National Geographic Institute installed the plaque on the first step of the Town Hall in 1874.

At that time, it was necessary to unify the measurements, so the small tidal range and the recent constructions in port and railway infrastructures in the city led experts to choose Alicante.

Once the point was marked, for four years (1870-1874), a technician from the National Geographic Institute recorded the readings that the sea level displayed on a metal ruler located on the Queen's Stairs. The average of this calculation placed the sea level at 0.430 meters above the mentioned ruler. To reference this measure, it was leveled from the Port's Tide Gauge to a circular bronze mark with the inscription NP1. It is located on the first step of the main staircase of the baroque-style Town Hall building in Alicante. Its elevation relative to the average sea level, calculated from the port, is 3.409 meters.

Thanks to this system, railways, roads, bridges, hydraulic infrastructures, and other public works that transformed 19th and 20th century Spain were built.

And this exact point is considered the origin of altitudes in Spain, as stated in the Royal Decree regulating the Geodetic Reference System in Spain. It is from this point that the different altitudes of the rest of the cities in peninsular Spain are obtained. Some of these readings are on the plaque located on the Town Hall's staircase. They are, for example: Mount Bencantil (169 meters above sea level), the Aitana mountain range (1,158 meters), or the Mulhacén Peak in Sierra Nevada (3,479 meters).

To blow out the candles, the event '150th Anniversary of the Origin of Altitudes in Spain' was held this Monday, organized by the National Geographic Institute, led by Lorenzo García Asensio. The event was attended by the Mayor of Alicante, Luis Barcala, the Undersecretary of the Ministry of Transport, Rafael Guerra, and the President of the Port Authority, Luis Rodríguez.

Barcala, in his speech, called for «recovering the names of the people who, with their hard, exhaustive, and precise work, contributed to this milestone and that, 150 years later, their research and study work remains fully valid.»

Finally, the two tide gauges installed in the port were visited, one of them operating since 1925 and which, although with more modern instrumentation, continues to operate today. The second tide gauge, built in 1956 and also operational, also has a fundamental GNSS station. Commemorative plaques were unveiled on both tide gauges, remembering this anniversary.

«This celebration is accompanied by the recognition of the work carried out by the National Geographic Institute in Alicante since the 19th century when, from the Queen's Stairs of the port, the readings that the sea level had were recorded, until reaching the 3.409 meters that appear on the access staircase to the Town Hall,» concluded the mayor.