In the middle of New Orleans, there’s a green space on Perdido Street, beside Duncan Plaza. No marker, just some parked cars. But about a hundred years ago, it was the site of one of the most important moments in jazz history. Louis Armstrong was about four or five years old, living with his mother at the corner of Liberty and Perdido, just a couple steps away from a building that stood right here. That building was the Union Sons Hall. Sunday mornings it served as the First Lincoln Baptist Church.