In 1866 I began a course of lectures at our Istituto Superiore on the History of Florence, chiefly for the purpose of examining the political constitution of the Republic, and investigating the various transformations it had undergone during the long series of internal revolutions by which the city was harassed. In this way I hoped to ascertain the veritable causes of those revolutions, to discover some leading thread through the mazes of Florentine history, which even when treated by great writers has often been found exceedingly involved and obscure, and likewise to determine the most logical mode of arranging it in periods. Even a partial solution of these problems would have been of some use. I continued the lectures for a considerable time, but suspended them on reaching the period of Giano della Bella's "Decrees of Justice" (_Ordinamenti di Giustizia_), 1293. Some of these discourses were published in the Milan _Politecnico_, others in the _Nuova Antologia_ at Florence. It was then my intention to collect them in a volume; but after some hesitation I renounced the idea. It seemed indispensable to at least add some outline of the course of events subsequent to the fall of Giano della Bella and the exile of Dante, in order to conclude the first and most important period of the political history of Florence. Besides, I saw that the necessity of continuing these lectures on fixed days had not always allowed sufficient time for overcoming obstacles encountered by the way. Accordingly, more than a superficial revisal was required; gaps had to be filled in, certain pages re-written. Hence fresh researches were demanded, for which other labours granted no leisure at the moment. Meanwhile new documents, new dissertations, and monographs on Florentine history were continually appearing, besides notable works on a larger scale such as those of Capponi, Del Lungo, Hartwig, Perrens, &c. All this increased the difficulty of revising and correcting lectures, now lapsing inevitably more and more out of date. On the other hand I sometimes found previous deductions confirmed by recently discovered documents, and that certain general ideas I had enounced were accepted and followed by writers of note. This naturally inclined me to be less severe in judging my work, and more disposed to listen to the tried friends who were urging its republication. Being thus encouraged to resume my forsaken studies, I lectured in 1888 on the times of Henry VII. of Germany and the exile of Dante. Later on, in 1890, recognising that my previous work on the origins of the city and its commonwealth had become altogether inadequate since the appearance of so much new material, I returned to the subject in a fresh course of lectures, which likewise saw the light in the _Nuova Antologia_. Then, I finally began to put the scattered papers together to revise and correct them.