The original Euro symbol was a mathematical construction, all measurements and curves. However, this posed a typographic problem: "Had the Eurocrats consulted a typeface expert, they would not have failed to learn the difference between a character's graph and its ductus. In a letter - and that's what the Euro sign is intended to be - its skeletal shape (graph) and actual form (ductus) are two different things".
There are some good quotes in Jürgen Siebert's article The Euro: From Logo to Letter. Here's another one: "Width, breadth of stroke and style are not elements of the A-ness of an A".
Micro-management of the symbol made it difficult to adopt -- how to make this sign have the same feel as another type, the correct shape, size, weight, contrast, serif? The highlight of the article is about 75% of the way down, a comparison of the newly designed Euro letter in context against uppercase numerals in nine different faces. The art of typography is to become invisible, and it's impressive seeing that evolution.