Decline and Fall is a four-player game in which some of the forces which led to the breakup of the Roman empire are represented. Each player is provided with counters representing peoples or armies which move across a map of the ancient world and engage in conflict with other units. Through strategic movement, conflict and diplomacy each player tries to achieve certain goals.

A game consists of 15 turns, each divided into 4 player-turns which in turn consist of three main stages: movement, conflict, and movement again. A full turn represents about 5 years of real time.