Swedish historian Ulf Sundberg’s excellent thesis published in 2018, “Swedish Defensive Fortress Warfare in the Great Northern War 1702-1710,” is available to read on academia.edu and several other places. It is over four hundred pages long, so rather than trying to paraphrase, I will list bullet points of the bits that were interesting to me and give the page numbers. The source is listed at the bottom of this post.
— A given fortress only controlled an area with the diameter of the reach of its best cannons, a few kilometers in the eighteenth century, or within reach of the riders housed within the fortress (Sundberg 62-63).
–The purpose of a moat, wet or dry, was to make it more difficult for the enemy to set up battering rams near the walls or ladders to climb the walls (68).
–Medieval fortresses had steep walls with moats. The advent of gunpowder and artillery brought sloping walls called glacis with bastions, or often triangular artillery platforms that stuck out so there would be no blind spots. Fortresses built between 1600 and 1720 usually had bastions. The earliest bastion fortress in Scandinavia is Uppsala Castle, which dates from the time of Gustav Vasa (68).
–A French engineer name Vaubon pioneered ricochet fire, in which attackers would aim low on the bastion walls so the cannonballs would bounce and take out the defenders artillery. Some fortresses had added a second layer of walls to protect against ricochet fire (69-70).
–Sundberg’s list of potential ways to besiege a fortress includes several I’ve only read about in medieval historical fiction, but are apparently legitimate from the sources listed. Enemy soldiers hiding in merchant’s wagons to enter a fortress, forging a letter from the fortress nation’s king requiring surrender, or planting a spy posing as a host nation soldier to open the gates and let the enemy (89-90).
–Moving artillery required a large number of horses (88)..
–A chamade was a signal given by either drum or trumpet during a siege battle to signal a willingness from one side to negotiate or surrender (98).
SOURCE: Sundberg, Ulf. “Swedish Defensive Fortress Warfare in the Great Northern War 1702-1710,” 2018. [read via paid subscription to academia.edu] This citation from academia.edu seems rather limited, so I will also note that the thesis is from the Åbo Akademi University Library in Finland.