The word "diet" is now used in English for the _Reichstag_, "imperial diet" of the old Holy Roman Empire; for the _Bundestag_, "federal diet," of the former Germanic confederation; sometimes for the _Reichstag_ of the modern German empire; for the _Landtage_, "territorial diets" of the constituent states of the German and Austrian empires; as well as for the former or existing federal or national assemblies of Switzerland, Hungary, Poland, &c. Although, however, the word is still sometimes used of all the above, the tendency is to confine it, so far as contemporary assemblies are concerned, to those of subordinate importance. Thus "parliament" is often used of the German _Reichstag_ or of the Russian Landtag, while the _Landtag_, e.g. of Styria, would always be rendered "diet." In what follows we confine ourselves to the diet of the Holy Roman Empire and its relation to its successors in modern Germany.
The origin of the diet, or deliberative assembly, of the Holy Roman Empire must be sought in the _placitum_ of the Frankish empire. This represented the tribal assembly of the Franks, meeting (originally in March, but after 755 in May, whence it is called the Campus Maii) partly for a military review on the eve of the summer campaign, partly for deliberation on important matters of politics and justice. By the side of this larger assembly, however, which contained in theory, if not in practice, the whole body of Franks available for war, there had developed, even before Carolingian times, a smaller body composed of the magnates of the Empire, both lay and ecclesiastical. The germ of this smaller body is to be found in the episcopal synods, which, afforced by the attendance of lay magnates, came to be used by the king for the settlement of national affairs. Under the Carolingians it was usual to combine the assembly of magnates with the _generalis conventus_ of the "field of May," and it was in this inner assembly, rather than in the general body (whose approval was merely formal, and confined to matters momentous enough to be referred to a general vote), that the centre of power really lay. It is from the assembly of magnates that the diet of medieval Germany springs. The general assembly became meaningless and unnecessary, as the feudal array gradually superseded the old levy _en masse_, in which each freeman had been liable to service; and after the close of the 10th century it no longer existed.
