The reconstruction of the covered markets, which until the arrival of Baltard were composed of anarchic and dilapidated buildings, brought a long and complex story to completion. This project, the necessity of which had been apparent for a long time, was initiated in practical terms by the municipal councillors under the July monarchy. Baltard began thinking about it from the beginning of the 1840s. In 1845, after having proposed a first project at the request of the administration, he was officially appointed as architect of the covered markets. But the challenges of this construction were such that they stimulated competition.
The most serious of Baltard's rivals was Hector Horeau, a visionary architect, whose project was studied and finally abandoned. On 3 June 1853, the worksite, which had begun in September 1851, underwent a dramatic turn of events: during a visit, Napoleon III discovered the monumental stone facade of the first building and imposed a halt on the work. This unforeseen development caused more than 40 alternative projects to be put forward, seriously calling Baltard into question.
Baltard's reaction was not long in coming. Ten days after the worksite was shut down, with his associate Félix Callet, he proposed three new projects including one making exclusive use of metal. In fact, he had been considering the use of this material for a long time.
Following the example of the most innovative constructions of his period, such as Henri Labrouste's Sainte-Geneviève library which was begun in 1843, Baltard's designs for the covered markets included an elegant metal structure surrounded by masonry, more or less visible depending on the proposals. Thanks to the support of Haussmann, who took charge of the Seine prefecture at the end of June 1853, his project for buildings made of metal and cast iron was endorsed. In spite of this final success, this episode would leave an indelible mark on Baltard's career: he would long be suspected of having copied his main competitors.