Passage: Having collected abundant booty and numerous slaves, in the autumn Scipio moved to Utica. His intention was to capture the ancient Phoenician city and make it a base for his further operations. The direct assault on the walls was repulsed even though it was supported by siege engines and the Roman fleet, so that the Romans had to undertake a regular siege of the city. The emergence of two large enemy armies effectively ended the siege very soon. These were the forces of Hasdrubal Gisgo and his son-in-law Syphax, who apparently did not hesitate anymore. According to the tradition passed by ancient authors such as Polybius and Livy, the army of Hasdrubal amounted to more than 30,000 and that of Syphax was twice the size,. but these numbers are considered as exaggerated by modern researchers, who estimate a combined Carthaginian-Numidian strength of 33,000–47,500. The two armies forced Scipio to retreat to a promontory not far from Utica, which was later called Castra Cornelia. He fortified the narrow neck of land and set his winter quarters, relying on supplies of corn and clothing that were being sent to him from Sicily, Sardinia and Iberia. Hasdrubal and Syphax built their separate camps some distance from Castra Cornelia.

Question: Who had to assume a seige?
the Romans