THE RICHEST DYNASTY IN HISTORY

That's the recurring question in Niall Ferguson's formidable The House of Rothschild, a history of the legendary European-Jewish banking family. ''There is but one power in Europe and that is Rothschild,'' said a French journalist in 1841, giving voice to the popular suspicion that the dynasty and its money held sway over the affairs of nations. In this first of a two-volume study (the second is due out next year), Ferguson confirms that often, the Rothschilds were behind the scenes, influencing policy across Europe in their own interest. However, the Oxford don also shows the clear limits to their power. With access to all extant Rothschild archives, Ferguson is well-positioned to separate myth from reality.

What has to be explained is how the Rothschilds rose so high from the obscurity of Frankfurt's 18th century Jewish ghetto. Seemingly overnight, they lifted themselves from Mayer Amschel Rothschild's coin dealership to become the world's richest family, with financial operations run by his five sons in London, Paris, Vienna, and Naples, as well as Frankfurt. Ferguson calculates that in relative terms, they were richer than any dynasty today--even the Saudi royal family.

That meteoric rise spawned several myths. In the first, Mayer Amschel was said to have hidden the fortune of William IX, ruler of the German principality of Hesse-Kassel, from the Napoleonic invaders and been rewarded with its long-term use. In fact, Mayer sheltered only routine papers. It was his son Nathan's leveraging of William's English investments that later helped make the Rothschilds a power in the City of London and on the Continent.

The most widespread Rothschild myth was that Nathan, after receiving news by carrier pigeon of Wellington's victory at Waterloo, made a vast fortune speculating on the rise in British government securities. The reality, says Ferguson, was quite different. The Rothschilds' couriers did alert them first to Napoleon's defeat, but since they had bet big on a protracted military campaign, any quick gains in bonds after Waterloo were too small to offset the disruption to their business.

Rothschild capital did soar--but over a much longer period. Nathan's breakthrough was a deal to supply cash to Wellington's army in 1814. Waging a high-risk campaign of exchange-rate transactions, bond-price speculations, and commissions, the family garnered huge profits from this governmental financing. Then, from 500,000 pounds in 1818, Rothschild capital rose to 4,330,333 pounds in 1828--about 14 times the resources of their nearest competitor, Baring Brothers, which had been a close second. Their strategy: financing the postwar stabilization of Europe's conservative powers. That meant luring monarchs and ministers, such as Austrian Chancellor Metternich, into their orbit. What made the Rothschilds ''the dominant force in international finance after 1815'' was ''the sheer scale--and sophistication--of their operations.''

One key to that scale was unity, a virtue that Mayer Amschel inculcated in his sons. That unity allowed the brothers--Nathan, James, Salomon, Amschel, and Carl--to run independent operations essentially as one firm stretched across Europe. Another advantage: By issuing foreign bonds in sterling, says Ferguson, the Rothschilds did much to create the international bond market. And as they returned profits to the firm, excluded ''outsiders''--in-laws, women, even their sisters' sons--and married off their children to first cousins, they added to their capital.

What these kings of the bond market craved was peace and stability, and they avoided lending to belligerent or unstable states. As Ferguson notes, however, there was an internal contradiction: The primary reason for states to borrow money was to wage war, which was what the Rothschilds worked to prevent in order to protect the bond market. One way out of this trap: moving into railway shares, which they saw as ''surrogate state bonds.''

The Rothschilds could be vulnerable. Fame brought a barrage of ugly anti-Semitic attacks. And despite their fear of instability, the Rothschilds were unprepared in 1830 and 1848, surviving the 1848 revolution only because of a timely silver shipment from their semi-independent New York agent, August Belmont. The rescue serves as a reminder of their biggest strategic error: the lack of a major U.S. operation.

Ferguson's fluid, masterful synthesis of a vast amount of material tends more toward the academic than the popular. But he brings vitality to a series of compelling issues, ranging from the Rothschilds' staunch Judaism to their intrafamily marriages. He makes brilliant use of literary sources from Disraeli to Balzac, and he is insightful about the Rothschilds' friendship with such musicians as the composer Rossini. Nathan and James come across as rude, hard-driving businessmen. It's not always a pretty picture, but by revealing what the Rothschilds were really like, Ferguson is better able to explain their achievement.

Were the Rothschilds pacifists, pillars of conservative monarchies, or, as the poet Heinrich Heine wrote, agents of a new revolutionary force, money? Chameleon-like, the Rothschilds were all--and none--of these things. For them, it was just business.