Although commonly remembered for the fortifications he built, Vauban's greatest innovations were in the field of offensive operations. Some years before the capture of Maastricht he had expressed his thoughts on siege warfare in a manuscript, that after his death, in 1740, was published under the title "Mémoire pour servir d’instruction dans la conduite des sièges et dans la défense des places". This has provided modern researchers some insights about the general principles de Vauban probably applied. The 'siege parallel' had been in development since the mid-16th century but Maastricht saw him bring the idea to practical fulfilment. Three parallel trenches were dug in front of the walls, connecting the perpendicular assault trenches, the earth thus excavated being used to create embankments screening the attackers from defensive fire, while bringing them as close to the assault point as possible (see Diagram). The transverse parallels allowed a much larger number of troops to participate simultaneously in an assault to overwhelm the defenders, while avoiding choking points that often had led to costly failures. Artillery was moved into the trenches, allowing them to target the base of the walls at close range, with the defenders unable to depress their own guns enough to counter this; once a breach had been made, it was then stormed. This remained the standard for offensive operations until the early 20th century.