Originally published in 1979, Martines's study of the rise and fall of the city-states in Italy, especially of its cultural manifestations (literature, art, architecture, political theory, and the philosophy of humanism), has for the most part withstood the test of time. The volume is not really an introductory survey for lay readers, nor is it a scholarly monograph. (In fact, the usual scholarly apparatus--notes and so on--is astonishingly sparse.)
Instead, the volume will serve as an overview for advanced undergraduates and specialists, summarizing the scholarship to date, integrating Martines's views on the interactions between economic class and cultural production, and presenting a largely revisionist analysis that portrays the Italian republics not as beacons of democracy or humanism (in the modern sense of the words) but as oligarchic structures alternating between periods of chaos and political stability.
Martines does not even broach the Renaissance era for the first third of the book. Instead, he develops the rise of the city-states during the eleventh through fourteenth centuries. It's the weakest part of the book, largely because his discussion is so filled with series of vague generalizations and with laundry lists of the common characteristics (or distinctions) across a swath of cities. Only occasionally does he depart from abstraction to mention specific historical examples, and for the uninitiated this first hundred pages will make torpid reading.
The meat is in the later sections of the book. At the risk of oversimplification, Martines's basic points are (1) that the political and military forces driving the city-states were defined by and developed for competing oligarchies (e.g., nobles against merchants, or one city against another) and (2) that the flowering of humanism was entirely at the service of those oligarchies. In short, a "Renaissance man" was a member of the upper class. Among historians today, these are hardly controversial tenets, but Martines shows how the attitudes and prejudices of the upper classes pervaded every aspect of life and art, from the "grandeur and show, order and ample spaces, finesse and finished surfaces" of architectural design, to the pragmatic ("realist and utopian") political visions of Machiavelli and Guicciardini, to the "relaxed and civilized" idealism portrayed by Castiglione's handbook for courtiers.
Martines's work serves as a partial rejoinder to those generalists (for example, Jacques Barzun, Daniel Boorstin) who still see the Renaissance primarily for the flowering of republicanism and humanism. Italy's art, culture, philosophy, politics, and militarism--all were at the service of the wealthy, and all were formulated to insure the continuing domination by those elites. Only much later were artists, historians, and scholars able to sift through this heritage for its potential republican virtues.