Stonehenge’s layout holds clues.
Above the trilithons is a pattern of four equally spaced parallel lines. This explains why the trilithons are located as they stand. The lines shown here represent four roof trusses.
The position of these trusses, at opposing ends of trilithon cap-stone is structurally sound. Their weight, plus anything they support acts though the trilithons together. These trusses spanned a central void, a large hall used for gatherings.
Stonehenge’s stones tell us it’s builders were planning something big and magnificent.
Trusses were formed at ground level and raised.
Raising trusses in this manner can only be done if the stone beneath is hard and immovable. This explains why sarsen stone was chosen – why so much effort went into quarrying and moving the megaliths that remain today. Softer stone would crumble.
The diagram above shows why the trilithons are different heights. Raising four trusses cannot be done easily if adjoining pairs of trilithons are of similar height.
Though big the roof span at Stonehenge was not impossibly large. Westminster Hall is much wider!