A google search in Spanish returned a Spanish site that indicated that "ORBEA y CIA" started producing bikes in 1926. A relationship with Zeus or a coincidence? Orbea was founded in 1860 and was a maker of firearms.
The website provides additional information as below. It wasn't totally clear to me if these are Basque-region only manufactures or not. In any case, it looks like the Basque region does have a rich history in cycling.
The site refers to these as manufactures "being important in their days": "Nicolas Arregui", "Zeus", "Echasa-Fenix", "Cil", Gamma o Abelux.
These auxiliary parts manufacturers are mentioned: "Triplex", "Iris", "Norma", Garechana, "Suar", "Hermógenes Larrañaga", "El Tigre", "Ges".
The bike shops, for sales and repairs, are mentioned: "Cancio Bilbatua", "Salaberria", "Askasibar" o "Juaristi".
This is the website (photos plus trophy from 1936 race):
http://www.egoibarra.com/
> CR Folk:
>
> Every Zeus catalog says "since 1926", and the 1977 catalog has a 50th
Anniversary emblem in it, so I used to think that Spanish cyclists were
buying Zeus parts in 1926.
>
> But the painting of the original place of business shows a shop with the
family name on it (Arrequi, or am I forgetting the proper spelling?) and
since the earlier components are branded Alfa and Super Alfa, I've been
wondering when the "Zeus" brand actually materialized.
>
> I've never seen pictures of Zeus bikes that looked like they were older
than perhaps the 60's, and I've never heard old-timers on the list
discussing pre-War or post-War Zeus this and that.
>
> Anybody heard of a Zeus bike or parts from the 50's? 40's? 30's?
>
> Just curious
>
> Brad Stockwell
> Palo Alto