The meaning of the term all'antica when applied to art and architecture, is that which 'imitates the style of the ancients. At the time, the Renaissance style of art and architecture was viewed by contemporaries in terms of the "all'antica," or that which was produced in an ancient manner; namely in the style of the Romans. All'antica can be seen as art and architecture which was produced in the Renaissance period, taking its influence from the art of classical antiquity and in the process imitating it, as ancient works of art were viewed as the ideal.
Summary: All'antica - in the manner and style of the ancients.
all'antica - in the mode of the ancients