Investment is the military process of surrounding an enemy fort with armed forces to prevent entry or escape. It serves both to cut communications with the outside world and to prevent supplies and reinforcements from being introduced.

The Sicilian Expedition was an Athenian military expedition to Sicily, which took place from 415–413 BC during the Peloponnesian War between Athens on one side and Sparta, Syracuse and Corinth on the other. The expedition ended in a devastating defeat for the Athenian forces, severely impacting Athens.