From Populous Wiki
Stone Heads are mystical statues left on the worlds by The Ancients. If they are worshiped, they will produce a reward of new skills that you can use to conquer the Enemy. Powers gained from Stone Heads only provide a single use, but more can be accumulated. If the new skill is a spell, it will only be able to be cast once, and if it is a building, it will only be able to be constructed once. Right-clicking on a Stone Head will show how many Followers are needed to worship the stone to begin. When a Stone Head is completely drained, it will sink into the ground. Right-clicking on the Stone Head while it is being worshiped will show a red line next to the number of Followers indicating how long it will take. Once it has finished, the worshiper will be awarded a new skill, although the Followers will continue worshiping until commanded them to stop.