Image: Iravatham Mahadevan
Image: Iravatham Mahadevan

An equilateral triangle is used to illustrate the concept of rotation. The triangle rotates around a fixed central point.

The triangles in Mahadevan's sign number 233 were not drawn with perfect precision. However, you can see from the diagram on the left how the equilateral triangle traces a circle as it moves.

Thus geometry gives us the verb to turn.

Illustrative Text Reference:

Harappa: Seal: H-477 A (NB. Image A is a mirror of the image that would appear on a sealing.): Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and Inscriptions: Volume 2: Page 281: Collections in Pakistan: Suomalainen Tiedeakatemia.

Image Credits:

Indus Script Sign Number 233: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.


Rotation of an Equilateral Triangle: Lynn Fawcett, 2017.