What is "diet of spires"

Diet \Di"et\, n. [F. di[`e]te, LL. dieta, diaeta, an assembly, a day's journey; the same word as diet course of living, but with the sense changed by L. dies day: cf. G. tag day, and Reichstag.] A legislative or administrative assembly in Germany, Poland, and some other countries of Europe; a deliberative convention; a council; as, the Diet of Worms, held in 1521. Specifically: Any of various national or local assemblies; as,

1. Occasionally, the Reichstag of the German Empire, Reichsrath of the Austrian Empire, the federal legislature of Switzerland, etc.

2. The legislature of Denmark, Sweden, Japan, or Hungary.

3. The state assembly or any of various local assemblies in the states of the German Empire, as the legislature (Landtag) of the kingdom of Prussia, and the Diet of the Circle (Kreistag) in its local government.

4. The local legislature (Landtag) of an Austrian province.

5. The federative assembly of the old Germanic Confederation (1815 -- 66).

6. In the old German or Holy Roman Empire, the great formal assembly of counselors (the Imperial Diet or Reichstag) or a small, local, or informal assembly of a similar kind (the Court Diet, or Hoftag).

   Note: The most celebrated Imperial Diets are the three following, all held under Charles V.:

   Diet of Worms, 1521, the object of which was to check the Reformation and which condemned Luther as a heretic;

   Diet of Spires, or Diet of Speyer, 1529, which had the same object and issued an edict against the further dissemination of the new doctrines, against which edict Lutheran princes and deputies protested (hence Protestants):

   Diet of Augsburg, 1530, the object of which was the settlement of religious disputes, and at which the Augsburg Confession was presented but was denounced by the emperor, who put its adherents under the imperial ban.