Very often the seminal text for a topic can be 'an old book'. For instance, how can you not read the Italian Renaissance with reading Burckhardt's magisterial The Civilization of the Renaissance in Italy ((iirc) 1860). It's one of those works that is largely out of date, misconceived, deeply flawed; but yet, remains a 'must read' cornerstone of the literature. It's beautifully written and describes a renaissance that is far more attractive and colourful than it really ought to be. Burckhardt describes Italian culture as if 'awakening from under a veil of sleep' (or something like that). The implication being that the Middle Ages had little to no culture. However, as easy as it may be to criticize this work, it is still one of the most important works on the Italian Renaissance.