With the holidays now past, today is the first day at work for the euro. From France to Greece, Portugal to Finland, 12 of the world’s developed economies now are joined together by a common currency.

It is the biggest such conversion in history, one that directly affects more than 300 million people and that immediately creates the second most important money on Earth. If – actually, when – European Union holdouts Britain, Sweden and Denmark adopt the euro, experts predict it will challenge the primacy of the American dollar within a decade.

This comes, of course, at a cost. Gone are the lira, francs, marks and drachmas, with their dashes of local color, miniature history lessons and wallet-sized doses of culture.

But the color, history and culture still will be there – they’ll just have to be found where they truly exist and not in representations on bills and coins.

The differences between Maine and New Mexico or Florida and Oregon thrive despite the common currency here; there is no reason to believe the same will not be the case in Europe. The benefits far outweigh the cost. Travel will be significantly easier – imagine driving from Bangor to Boston, with a pit stop in Portsmouth, and having to convert Maine money twice along the way, calculating exchange rates and paying 5 percent bank fees each time. Consumers will gain price transparency, the ability to compare what merchants in, say, Spain and Ireland charge for the same item. The result of this transparency already became evident during the euro’s three-year trial run in a key economic indicator called the Big Mac Index – prices for McDonald’s trademark sandwich used to vary across the EU by as much as 75 percent. Now, the difference has shrunk to 37 percent.

Even greater will be impact on economic development. All 12 euro nations are bound by interest-rate decisions of the European Central Bank in Frankfurt, the same way all Americans are bound to the Federal Reserve. The elimination of exchange-rate swings will help manufacturers in smaller economies in their dealings with larger-economy providers of raw materials – an Italian carmaker buying German steel, for example. Bond markets, an essential source of capital for growth, already have responded favorably to the clout of this new economic powerhouse.

But the most profound impact of the euro goes beyond the fiscal. It is concrete

evidence of the integration of Europe,

a genuine manifestation of Churchill’s

dream a half-century ago of a “United States of Europe.” For a continent that nearly destroyed itself twice in world wars, a jingling reminder in every pocket that cooperation can replace conflict is priceless.