The huge rectangle of the Champ de Mars lay about a mile south of the Arc de Triomphe, just across the river on the Left Bank. Until the eighteenth century, it had been a pleasant quarter of market gardens and allotments. But then a big military school was built along its southern edge, and the gardens running from the school to the Seine became a parade ground, and a site for great gatherings after the Revolution. The place had been made even more splendid a few years later when, to celebrate one of his many victories, the emperor Napoléon had ordered a fine bridge, the Pont d’Iéna, to be built across the Seine directly opposite the place. So the Champ de Mars had been an excellent choice for mounting the World’s Fair of 1889. People would be able to walk across the Pont d’Iéna to the Left Bank and then directly under Monsieur Eiffel’s astounding tower whose four, splayed iron feet would form the colossal entrance arch.

Everything had been set. Except for one thing.

Thomas remembered the day his father had come in with the news.

“Your friend Monsieur Eiffel has a problem,” he’d announced. “The city has told him to build his tower, but they’re giving him only a quarter of the money.”

“So who’s paying for it?”

“Eiffel. He’s got to pay for the tower himself.”

It was an extraordinary situation. To celebrate the centenary of the French Revolution, the city of Paris had ordered a tower and refused to pay for it.

But if Eiffel was a great and inventive engineer, he now showed that he was an entrepreneur of huge courage and vision. “Give me the right to the first twenty years of the tower’s earnings,” he said, “and I’ll find the money.”

So as Thomas approached the empty building site, he knew that before him lay not only the pride of France, but the financial triumph or ruin of Monsieur Eiffel himself.

In front of Thomas now was a huge field of mud. The great 136-yard square that would be the footprint of the tower was marked by huge trenches at the four corners—north, south, east and west—where crews of laborers were busily digging.

He started to walk onto the site to take a look. A man in an overcoat and bowler hat rushed over and told him sternly that he must leave. But after Thomas explained that he had worked for Monsieur Eiffel on the Statue of Liberty, and that he’d been sick, the man became friendly and offered to conduct him around.

They looked first at the two big excavations at the southern and eastern corners, where one could already see, at the bottom of the pit, a good, dry base where the concrete foundations could be poured. Then they walked over to one of the riverside diggings. And Thomas gasped.