You will begin as a low ranking Roman bureaucrat, and must work your way up towards the final goal of --what else-- the Emperor's throne. You will be given control of a pristine Roman province, which you must develop into a thriving metropolis to gain promotion to other provinces that are progressively larger and more difficult to rule. Promotion requirements for each province encompass military might (i.e. successful defense of the province against enemy attacks), as well as economic and social goals (e.g. population happiness and health).
What makes Caesar a lot of fun to play is its tongue-in-cheek inclusion of Roman culture and mythos. You can hope for divine favor buy building temples, and build the coliseums to please the people. Historical elements also strike a good balance between playability and realism: you need to build baths for health-conscious populace, foster industrial growth by trading with neighboring provinces and encourage industries with natural advantages (e.g. wine in Southern Italy). In a novel twist to typical wargame design, the game can even be interlocked with Impressions' Cohort II to give you greater control over tactical battles. Caesar is the game that finally puts Impressions' name on the map of quality strategy game companies to watch for, although it was still quite underrated in its days due to poor distribution and lack of fanfare. Best of all, Impressions has decided to give away the game for free, to cheers of all fans, although unfortunately the manual isn't up for download (you can get it here, however). Two thumbs up!