This elusive monument is classic, early Christian, Byzantine, Lombard or Romanesque? Is it really an ideal model of perfect unity or has been transformed in several times? And moreover: it's born as a true baptistery or - perhaps - it was once a 'Temple of Mars'? Although studied for centuries in every aspect by a crowd of scholars and historians, the topic of the origins of the Florentine Baptistery of San Giovanni remains debated and obscure, since the authors are divided between those who believe it ancient and those who medieval. Thus, being it still not related with certainty to a specific historical context, the «bel San Giovanni» loved by Dante does not find a ascertained and firm placement in the texts, and it is not even clear the role it played in the birth of the Florentine Renaissance. This book tries to give an answer to the lasting problem in a synthetic view that resumes documents and researches, pointing most of all to what the architecture suggests.