The initial period of French domination lasted until 1409, when the republic was ruled by the Marquis of Montferrat until 1413. The Duke of Milan Filippo Maria Visconti took power of the weakened republic between 1421 and 1435.During the 1450s and 1460s, the Republic became a pawn in the struggle between France and Aragon for power and influence in Italy. Christopher Columbus was born in Genoa c. 1451, but sought a career elsewhere. Threatened by Alfonso V of Aragon, the Doge of Genoa in 1458 handed the Republic over to the French, making it the Duchy of Genoa under the control of John of Anjou, a French royal governor. However, with support from Milan, Genoa revolted and the Republic was restored in 1461. The Milanese then changed sides, conquering Genoa in 1464 and holding it as a fief of the French crown. Between 1463–1478 and 1488–1499, Genoa was held by the Milanese House of Sforza. From 1499 to 1528, the Republic reached its nadir, being under nearly continual French occupation. The Spanish, with their intramural allies, the "old nobility" entrenched in the mountain fastnesses behind Genoa, captured the city on May 30, 1522, and subjected the city to a merciless pillage. When the great admiral Andrea Doria of the powerful Doria family allied with the Emperor Charles V to oust the French and restore Genoa's independence, a renewed prospect opened: 1528 marks the first loan from Genovese banks to Charles.Thereafter, Genoa underwent something of a revival as a junior associate of the Spanish Empire, with Genovese bankers, in particular, financing many of the Spanish crown's foreign endeavors from their counting houses in Seville. Fernand Braudel has even called the period 1557 to 1627 the "age of the Genovese", "of a rule that was so discreet and sophisticated that historians for a long time failed to notice it" (Braudel 1984 p. 157), although the modern visitor passing brilliant Mannerist and Baroque palazzo facades along Genoa's Strada Nova (now Via Garibaldi) or via Balbi cannot fail to notice that there was conspicuous wealth, which in fact was not Genovese but concentrated in the hands of a tightly-knit circle of banker-financiers, true "venture capitalists". Genoa's trade, however, remained closely dependent on control of Mediterranean sealanes, and the loss of Chios to the Ottoman Empire (1566), struck a severe blow.The opening for the Genovese banking consortium was the state bankruptcy of Philip II in 1557, which threw the German banking houses into chaos and ended the reign of the Fuggers as Spanish financiers. The Genovese bankers provided the unwieldy Habsburg system with fluid credit and a dependably regular income. In return the less dependable shipments of American silver were rapidly transferred from Seville to Genoa, to provide capital for further ventures. The Genovese banker Ambrogio Spinola, marqués de los Balbases, for instance, himself raised and led an army that fought in the Eighty Years' War in the Netherlands in the early 17th century. The decline of Spain in the 17th century brought also the renewed decline of Genoa, and the Spanish crown's frequent bankruptcies, in particular, ruined many of Genoa's merchant houses. In 1684 the city was heavily bombarded by a French fleet as punishment for its alliance with Spain.

Question: Where were these so called merchant houses?
Answer: Genoa