Milestones are significant events that are either reached within the plan (such as the completion of a phase of work) or imposed upon the plan (such as a deadline by which to apply for funding). Because the milestone itself doesn’t normally include any work, milestones are normally represented as tasks with zero duration. To visually distinguish milestones, their Gantt chart symbol appears as a diamond rather than a bar. However, you can flag any task of any duration as a milestone.