The fire caused by lightning in 1705 and the Lisbon earthquake of 1755 are the most important events to affect the structure of the Cathedral.
The subsequent restoration, which was necessary to strengthen the structure, and the traces left by both events (cracks, underpinning, iron bands, etc.) are today part of the history and architecture of the Cathedrals and their towers. The chapter of the Cathedral and the Town Council, together with other institutions and donations from private individuals, met the expenses as we are told by several edicts of the chapter meeting and contemporary accounts.
An eye-witness account of the fire of 1705 reads as follows: ….During a storm a bolt of lightning fell that damaged the upper part of the capital of the tower, which caught fire because it was made of wood and lined with lead… it reduced to ashes the whole of the capital, the wooden floors of the tower, and the clappers of all the bells. The bell of the clock fell into the street and was broken into many pieces; part of the handbell and a small bell melted. The small bells, even the largest of them, settled into the gaps in the walls of the Tower…despite the fact that no misfortune befell any of the many people of every station who gathered to relieve this sorry sight…
All the institutions threw themselves into helping the Cathedral, with the addition of a large amount of alms from private individuals. On 11th November the work to repair the tower had already been completed, but the lack of economic resources delayed the conclusion of the new ornamental top of the tower until 1710. Shortly afterwards the excessive weight of the baroque crowning caused the deterioration of the Romanesque shaft. These structural problems would subsequently be aggravated by the Lisbon earthquake of 1st November 1755, which left large cracks in the Bell Tower.
The earthquake that occurred on Saturday 1st November 1755, which was All Saints’ Day, at the time of high mass had an extraordinary impact at the time, as there were several thousand victims in Portugal, Spain, and North Africa and considerable material damage was caused. It was felt all over the Iberian Peninsula and in some other parts of western Europe and even in America. Its effects were also recorded on the Atlantic islands of Cape Verde, the Azores, Madeira, and the Canaries. The earthquake takes its name from Lisbon as this was the city most affected. The epicentre was located below the sea, which led to the formation of a huge tsunami that devastated the south-west coast of the Iberian Peninsula to cause even more deaths than the tremor itself. Several tremors occurred on the morning of 1st November 1755. The earthquake lasted for 2 minutes and reached a maximum intensity of 9 on the Richter scale. In Lisbon alone over 50,000 people died, not only as a result of the earthquake and subsequent tsunami but also in a huge fire that swept through the city. The tsunami devastated the Portuguese coast and the area of the Bay of Cadiz, in which town the force of the sea broke through the city walls and moved stone blocks weighing between 8 and 10 tons.
El alcalde mayor de Salamanca informaba el mismo día 1 de noviembre al Gobernador del Consejo, de los efectos del terremoto de Lisboa en Salamanca: «…se experimentó en esta ciudad un terremoto, cuya duración fue de 6 o 7 minutos, el que ha causado en general susto y consternación, por hallarse a la sazón los templos llenos de gente, que estaba oyendo la misa mayor…»
On that same day of 1st November the Mayor of Salamanca informed the Governor of the Council of the effects of the Lisbon earthquake on Salamanca: “…an earthquake was felt in this city that lasted for 6 or 7 minutes, which caused widespread alarm and consternation as at the time the churches were full of people attending high mass…” The edict that was passed on the orders of the Chapter referred to the impact of the tremor on the Cathedral on All Saints’ Day 1755 in the following terms: “… that at the end of the Gloria in excelsis of the high mass, the whole of the paving, columns, walls, and vaults of both churches suddenly shook with the crunching of all their workings, amazing the faithful with their continuous movement and exceeding the static balance, which because of its height made the Towers…”
The tremor was felt in the stonework of the Old Cathedral and New Cathedral of Salamanca and led to panic among those attending the high mass of All Saints’ Day: the bell even rang out on its own. The dome of the New Cathedral, the cloister of the Old Cathedral, and the Belfry Tower were the elements most affected. Despite the force of the earthquake, there were no victims to lament.
Other buildings and structures affected by the earthquake included the steeple of the Colegio de San Bernardo, the dome and towers of the Colegio de la Compañía de Jesús, the Church of San Sebastián, and the water mills of the River Tormes.