This article explores a feature of the geometry conveyed by architectural writings, in particular by Italian writings of the second half of the 16th century: namely the fact that mathematical instruments play a central role in it. How is this geometry to be placed as compared to the multiple mathematical traditions of the same period? It draws in fact simultaneously from the scholarly and the abaco tradition as well as from literature on practical geometry. In this respect, in order to present geometrical constructions, these writings create an alloy from the Euclidean »enunciation structure and the instruction sequence about how to manipulate instruments. In addition, the writings under scrutiny tend to expand, beyond the ruler and the compass, the arsenal of instruments used in geometrical operations. While being quite different in regard of format and status, the works by Pietro Cataneo, Sebastiano Serlio, Giuseppe Salviati, and Daniele Barbaro seem to share this tendency as a common trait. These features taken together, as will be argued, express the underlying understanding of geometry as a science dealing with the use of mathematical instruments, an understanding that can also be found in practical geometries of the period. Nevertheless, the writing technique used by these authors adopts approaches from the scholarly tradition as well as from the literature on practical mathematics.