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Stone Stories: Eggs and curd for mortar

Charles Bridge seen from Hradschin castle. Photos: Bertram Feld(December 2008) What used to be only a legend has now been confirmed: stone-masons added curd and eggs to their mortar when constructing Prague’s Charles Bridge in the 14th century. This was the finding of analyses by the Czech University of Chemical Technology (VŠCHT). The original mortar was discovered during reconstruction of the bridge. Scientists found substances containing protein. „It is possible to prove beyond reasonable doubt that eggwhite and milk or curd were used“ confirmed an expert of the university. Mixing protein in the mortar not only makes it harder but also slows the setting process thus having allowed masons more time to complete their work.

According to legend, Emperor Karl IV had ordered serfs throughout the country to bring eggs to Prague to help build the bridge. Construction began in 1357 and lasted about 50 years. The bridge spans across the Vltava river, joining both halves of the city. Its 10 m-wide 16 arches are made of stone stretching across a total of 516 m. Master builder of the time was the 27-year-old Peter Parler.

Endless legends are recounted on city-tours, like the one that the ground stone was laid according to precise astrological calculations on June 9th 1357 at exactly 5:31 a.m. so that the numerological sequence when reading year, month, day, and hour gives 1-3-5-7-9-7-5-3-1. The sequence not only comprises all uneven natural numbers but is also a palindrome symbolizing the mystical alpha and omega, or, pertaining to the bridge, the ideal hour of birth to withstand the ware and tear of time.

The Charles Bridge is, after all, one of the oldest stone bridges still standing today despite collapsing columns, world wars and floods.

Charles Bridge standing firm on its 16 columns.