Today is the Feast Day of Hild of Whitby, the anniversary of her death in 680. I mark the day because Hild—and Whitby, its abbey, and ammonites—has marked my life, and in particular my writing life.

My first novel was Ammonite, which was published when I was 32. The author photo I used for that book was taken at Whitby Abbey when I was 30. You can tell from the look on my face how much the place affects me.

In my third novel, The Blue Place, Aud talks longingly of Whitby—the abbey founded by Hild in 657. In Whitby you can find three species of fossil ammonites, or snakestones. A whole genus of ammonites, Hildoceras, is named for Hild: there is a legend that she turned all the local snakes to stone. The legend was so well-established after her death that in the later middle ages enterprising locals carved heads on the stones and sold them as the snakes she petrified.

This is Hildoceras bifrons (though to be frank I can’t tell the difference between this and H. lusitanicum and H. semipolitum). It’s what I think of when I think of ammonites.

Ammonites fascinate me: their shell growth, that lovely spiral, is guided by phi. And phi (Φ = 1.618033988749895… ), the basis of the Golden Ratio or Divine Proportion, has all sorts of interesting mathematical properties. The proportions generated by phi lie at the heart of myriad things: the proportions of graceful buildings, the orderly whorl of a sunflower, ammonites, Fibonacci numbers, population growth, and more. (If you’re interested, a good place to start is Wikipedia.) Phi is what creates the underlying pattern in much of nature. I think phi is responsible for what Hild may think of as God.

So tonight I’ll drink a toast to Hild, and ponder, as I always do, getting an ammonite tattoo.