The Gyrobifastigium

The gyrobifastigium (J26), also known by its Bowers Acronym gybef, is the 26th Johnson solid. It has 6 vertices, 14 edges, and 8 faces (4 triangles, 4 squares). It can be constructed gluing two triangular prisms together at their square faces in gyro orientation.

A gyrobifastigium

Its name comes from Latin fastigium, meaning roof, referring to the shape of a triangular prism resting on one of its square faces; bi-, meaning two; and the prefix gyro-, referring to two pieces being joined together in gyrated orientation. Hence, the compound gyro-bi-fastigium refers to the joining together in gyrated orientation of two roof-like shapes (triangular prisms).


In order to be able to identify the gyrobifastigium in various projections of 4D objects, it is useful to know how it appears from various viewpoints. The following are some of the viewpoints that are commonly encountered:

Projection Envelope Description

Top view.


Side view.


Diagonal side view.


The Cartesian coordinates of the gyro­bifastigium, centered on the origin and with edge length 2, are:

Last updated 08 Mar 2018.

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