MONOBLOCK CORNER in left photo - only one piece, monoblock. typical roman style. Taken from the frames of Medici and Salvator Rosa, from a single block of stone, can only be made by hand chiseling.
MITRE JOINT CORNER in right photo - two pieces. called "quartabono". While bonoblock can only be hand made chiseled, mitre joints allow the use of machines. The external corners are fragile, delicate and easily damaged.