This classic strategy game sees the player being challenged to take a civilization from a band of wander tribes man to a world dominating force. The basic concept is to build villages into towns and towns into cities. As your population grows you also need to research new technologies; technologies that will allow you not just to advance as a civilization, but also allow you to build better armies, to raise your population's consciousness to new religions, and erect magnificent monuments that build a sense of nationhood.

The game is wonderfully easy to play but awfully complex to master. It is a testament to Sid Meiers' genius that this game has largely remained unchanged in concept and gameplay from when it was first released some 15 years ago.

Civilization IV, which is required to play this expansion, was released almost a year ago now and in the the tradition of the series there was an expectation of at least one expansion pack. Civilization IV: Warlords is that eagerly awaited expansion. However it may appear a bit underwhelming: six new civilizations and six scenarios does not seem much of a expansion, but like the original game itself there is a lot of subtle changes and new challenges that at first glance go unnoticed.

The six new civilizations mark the welcome return of the Zulus, which have been a perennial favourite with players throughout the series. The Celts also make the cut. The Carthaginians, notably absent from the Civilization IV, are there - as is Korea and the Ottomans. Our favourite, though, is the Vikings, who are now ready to burst forth and claim their place in the world.

Each of these new civilizations includes its own unique leaders, including Hannibal, and Shaka of the Zulus. Some of the existing civilizations have also received new leadership options. The English now have Winnie (Winston Churchill) and the Romans have Augustus Caesar, to name a couple. Each of these leaders has specific traits which opens the door to more empire building strategies.

Each of the new civilizations has its own unique units while overall triremes and trebuchets have been added to units available to all. The trebuchets are designed to be city urban renewal artillery and are particularly effective earlier in the game at taking out units ensconced in a city. All civilizations now have the stable as a city improvement to allow mounted units, and also a monument, which is excellent for increasing your cities' influence in the early game phases.

That's not all, though; there is also a few new wonders. These epic structures that you can build to accrue enormous benefits to your civilisation now include the Great Wall, the University of Sunkore and the Temple of Artemis. The coolest one is the Great Wall, which once completed will protect you from those dreaded bands of Barbarians. When you have built it a huge wall appears around the borders of your entire civilization.

There's also a heap of new city items that are specific to each civilization, including the shopping mall for the Americans, the Dun for Celtics, and the Pavilion for the Chinese, to name but a few. The title of the game becomes clear with the new Warlord, or great general unit. Like other great units you can use it to either contribute an improvement to your city, or in the case of the Great General, lead your armies. Its presence accrues benefits to the surrounding troops. All in all there is a lot of subtle new additions that have added considerable depth to the game.

A lot of these new options really come to the fore when you look at the new scenarios. These are taken from the pages (parchment?) of ancient history and include the rise of Rome, the Vikings and Ghengis Khan. Each scenario has special rules and victory conditions. The best and probably the most welcomed is the ability to play the Barbarians. Yes, you to can now move your horde of Barbarians across the map and destroy burgeoning civilizations, pillage villages and gather wealth from your hapless victims.

The only unwelcome addition to this game is the occasional bug. Some of the wonders, when completed, don't seem to have a construction graphic - or it's skipped altogether. A small thing perhaps, but annoying nonethless to a player who has invested so much effort in building it.