...A hundred years ago, Galileo had to strive to establish the “new science”, the science born of experience and observation in the complete freedom to discover and spread different truths from those confirmed by tradition. For many years I, according to his teachings, have “read in the vast book of the Universe”, as he used to say – never tired of observing and experimenting, never sated with learning, if I may say so. Just as he was.

It was precisely here, in the Cathedral, that Galileo made his first dicovery.
Vincenzo Viviani, a disciple, tells us that one day young Galileo – not yet 20 years old - had the chance to observe the obscillation of a lamp hanging from the Cathedral’s ceiling. Availing himself of his pulse to reckon the time, he found that the obscillations all had the same duration although their amplitude was gradually decreasing. A discovery of capital importance for his subsequesnt studies.
The lamp is not the one you’re seeing now: it was replaced on the 20th of december, 1587, while Galileo’s observation took place four years earlier. The one credited with sparking off Galileo’s intuition was way smaller, and unpretentious…I don’t know what became of it.
The Cathedral itself, as Galileo saw it, was indeed different from what we can see now. That was before the great 1595 fire. Did anyone tell you about it?

It flared up at night, on the 24th of october, 1595. It was dreadful. There is an account of the event by a contemporary chronicler:
"On the night following the day of tuesday, the twenty-fourth of october of the year 1595 was the memorable fire in the ancient and venerable Cathedral of the city of Pisa"...
A master Giovandomenico of Milan, in charge of readjusting the lead slates of the roof covering, was its unwitting author by leaving some embers after his work was done. The old wooden beams of the roof easily worked as tinder, so that
"the lead subjected to the owerpowering heat from the fire slowly began to melt and liquefy and thus began to pour down from the eaves like water would...
The fire being so great the fumes were even greater and unimaginable the commotion and racket provoked by the crackling of the flames and the collapsing of the wood and the lead that cascaded outside along the eaves and in the church"...
The fire kept raging for eighteen hours; when it finally died down, it must have been a desolating sight:
"Left standing were the walls on the one side and the other with a vast amount of melted lead on the outside, along the eaves and in the middle all the columns scraped and cracked and the three naves and chapels with the bare walls and columns were so scorched as to be like lime to the touch, the Dome was still standing...The marble statues were left all scorched, blackened and broken here or there because of the half-burned beams falling on them from the roof…
The astonishement in the people was such, that the men were wandering the streets like half-dead and upon meeting each other they immediately hugged while crying and pleading each other for mercy and forgiveness as if it had been the end of the world. There was no one that opened shop or traded or went about a business whatsoever, but all that day in the wretched city no one did anything but painfully cry over the ruins of that church".