Some of them are known all across the world, but all of them are specially poignant in Sheffield, with most of them now marked by memorials to make sure that no one forgets.
We have put together a gallery, below, recalling these 12 days or dates.
1. Nine days that have gone down in Sheffield folklore
This gallery shows nine days that have gone down in Sheffield folklore, that most in the city know about. Photo: Sheffield Newpapers / Picture Sheffield
2. Sheffield Pals at The Somme, July 1 1916
The Sheffield Pals had been set up as a battalion of volunteers within the Yorkshire and Lancaster Regiment (12th battalion) near the start of World War One, with just over 1,000 members. They went into battle for the first time on the first day of the Battle of the Somme, near the village of Serre, on July 1, 1916. By the end of that day, 513 of them were killed, wounded or missing. Picture shows the Sheffield Memorial Park near Serre, at the Somme. Picture: David Kessen Photo: David Kessen
3. Sheffield Blitz, 12/13 and 15/16 December 1940
Almost 700 people were killed during the air raids of the Sheffield Blitz, which was 12/13 and 15/16 December during World War Two, as bombers attacked the city. Over 82,000 houses of a total stock of 150,000 were damaged. A number of well known buildings were also badly damaged or destroyed. PIcture shows buildings damaged by the blitz in Sheffield - High Street and The Moor Photo: ©Sheffield Newspapers Ltd
4. The Great Sheffield Flood, March 12 1864
The Great Sheffield Flood was a flood that devastated parts of Sheffield, England, on 11 March 1864, when the Dale Dyke Dam broke as its reservoir was being filled for the first time. At least 240 people died and more than 600 houses were damaged or destroyed by the flood. The picture shows a memorial to the victims The Great Sheffield Flood
12th March 1864 Photo: Sheffield Newspapers