Its vast bronze doors pictorially chart the island's history, and the immense main gallery inside has a diamond in the floor beneath the dome, symbolizing that now-distant era when Cuba was rich.
Its vast bronze doors pictorially chart the island's history from past poverty to current wealth. 
mnli hypothesis: Its vast bronze doors pictorially chart the island's history from past poverty to current wealth.  premise: Its vast bronze doors pictorially chart the island's history, and the immense main gallery inside has a diamond in the floor beneath the dome, symbolizing that now-distant era when Cuba was rich.