A process for preparing a polyazole with an inherent viscosity, measured in at least 96% sulfuric acid at 25° C., greater than 2.9 dl/g, comprising the steps of i) mixing one or more aromatic tetraamino compounds with one or more aromatic carboxylic acids or esters thereof which comprise at least two acid groups per carboxylic acid monomer, or mixing one or more aromatic and/or heteroaromatic diaminocarboxylic acids, in polyphosphoric acid to form a solution and/or dispersion ii) heating the mixture from step i) under inert gas to temperatures in the range from 120° C. to 350° C. to form the polyazole, wherein in step ii), a mixture having a concentration of polyphosphoric acid, calculated as P2O5 (by acidimetric means), based on the total amount of H3PO4, polyphosphoric acid and water in the mixture, greater than 78.22%, is heated, the amounts of the components are selected in step i) such that the proportion by weight of the tetraamino compounds and of the aromatic carboxylic acids or esters thereof which comprise at least two acid groups per carboxylic acid monomer, or of the diaminocarboxylic acids of the mixture in step ii), based on the total weight of the mixture, is less than 11.0% by weight, the reaction mixture is heated in step ii) to greater than 220° C.