E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Apex,
the topmost height, really means the pointed olive-wood spike on the top of the cap of a Roman priest. The cap fitted close to the head and was fastened under the chin by a fillet. It was applied also to the crest or spike of a helmet. The word now means the summit or tiptop.
