​As we said, Gernika was bombed on Monday, 26 April 1937, market day. There was quite an atmosphere of unease at the time, particularly in the wake of the recent bombardment of the nearby town of Durango, some 30 km from Gernika. Despite this the market went ahead as usual and, although it is difficult to establish any precise figures in this regard, a total of approximately 10,000-12,000 people were in Gernika that day. At 16:20 h, the bells of the Santa María church rang out to warn the local population of the approach of enemy aircraft. Most of the planes formed part of the German "Condor Legion", along with a smaller number from the Italian "Aviazione Legionaria". The aerodromes used as a base for the bombing mission were located in Vitoria, Burgos and Soria. After the warning had sounded, the people of Gernika ran to seek refuge in a number of shelters built for this purpose, where they stayed for almost four hours until the bombing stopped. The attack was incessant, with barely any intervals between the bombing waves, and the tactics used in the raid were as follows:

1. First bombers and a number of fighter planes were sent in to warn the people and force them into the shelters in the centre of town. The fighter planes then circled around the target to prevent anyone escaping from the town centre.
   
2. The first bombs dropped were break-up bombs weighing between 50 and 250 kg, to destroy the buildings. The bombs broke through roofs, forming enormous craters when they exploded on the ground. This exposed the entire structure and wooden features of the houses at that time. 
   
3. Incendiary bombs were then dropped. These were steel bombs weighing between 1 and 2 kg, and they contained an alloy of magnesium, aluminium and zinc which reacted when it came into contact with other metals to bring about uncontrollable fires reaching temperatures above 1,500 degrees. A huge fire thus engulfed Gernika, and was visible from villages many kilometres away. 
   
4. Finally, survivors attempting to escape from the town centre were machine-gunned by the fighters, diving to altitudes as low as 50 metres. They operated around the accesses to Gernika, flying in circles to keep the local people within the perimeter of the fire. The streets in the town centre were very narrow and the houses were built very close together, making it easier for the fire to spread. 
   

​More than 85% of the town was totally destroyed.