Take the following as truth: The 85-m- (267-ft-) tall bell-tower (it's a 414-stair climb to the top) is decorated on its lower sections by hexagonal bas-reliefs sculpted by Andrea Pisano and Luca della Robbia, based on Giotto's drawings.
Then the following statement: "Andrea Pisano and Luca della Robbia spent many years sculpting the lower half of the bell-tower." is true, false, or inconclusive?