One of my favorite Monty Python skits is "What have the Romans ever done for us?" Watch it here.
Those aqueducts, roads and bridges were built on a solid foundation. The Romans were masters of organizational structure. A great example is how they organized their military.
The basic unit of organization within a Roman legion during the time of Julius Caesar was the contebernium, a group of 8 legionaries who shared a tent. Legionaries began their careers as probatios, raw recruits. Once they passed muster and were deemed fit to serve they swore an oath and became tirones. They were now officially part of the military and subject to its rules, regulations and consequences for failure. After completing several months of intense training the survivors were graduated to the status of gregarii, soldiers.
The 8 gregarii were led by a decanus, a sergeant responsible for their ongoing supervision and development. 10 tents of 8 grerarii formed a century led by a centurion, assisted by an optio. 6 centuries formed a cohort, a cohesive group totaling 480 men. And, 10 cohorts formed a Legion. This structure had worked well since the founding of the republic 500 years before Caesar - no theory here.
Think about the span for the decanus. The Romans determined that 8 was the optimal number of people that he could effectively supervise and develop. What is the optimal number of people that the leaders in your organization can develop? Is it 6? 10?
Having a flat organizational structure may look good on paper but rarely plays out well in practice. Take a lesson from the Romans when building your organizational structure - your Accountability Chart™. Get it right. Whatever the number, ensure that your leaders have the responsibility, accountability and time to develop each person.