Military operations are told by the author with attention to detail: Turkish preparations with concentration and fueling a huge army headquarters, strictly speaking, taking the Golden Horn and final assault. The text is both "technical", with details of the Byzantine fortifications or characteristics of artillery and ships used in combat and epic. The heroism of the defenders, aware of the inexorable end of their world, is described with a poignant realism.
Crucially, Steven Runciman's book also focuses in its first chapters to explain the causes of the Byzantine decline and the rise of the Ottoman power, installed for several decades in Europe as well as in Asia Minor. Finally, the author devotes two chapters to the (sad) fate of the defeated population of Constantinople, massacred or enslaved, and the consequences of that capital for the future headquarters of the Mediterranean world. As factual and analytical, "The Fall of Constantinople" is therefore an excellent monograph to understand the magnitude of this historic event.
The book includes several maps and diagrams useful in understanding the text.