Saguntum stood as an outpost of Rome. While Carthage had been advancing from the south Rome had been pressing forward from the east along the shores of the Mediterranean, and had planted herself firmly at Marseilles, a port which gave her a foothold in Gaul, and formed a base whence she could act in Spain. In order to check the rising power of the Carthaginians there she had entered into a firm alliance with the Saguntines, whose country occupied what is now the district of Valencia. By the terms of the last treaty between the two republics each was forbidden to make war upon tribes in alliance with their rivals, and Saguntum being thus under the jurisdiction of Rome, an attack upon it would be almost equivalent to a declaration of war.
The position of the city was one of great strength. It stood on an almost isolated rock at the foot of a spur of the mountains which formed an amphitheatre behind it. Around it extended a rich and fertile country, the sea was less than a mile from its walls, and the Romans could thus quickly send succour to their allies. The rock on which the town stood was well nigh inaccessible, falling sheer down from the foot of the walls, and was assailable only on the western side, where the rocks sloped gradually down to the plain. Here the walls were extremely strong and lofty, and were strengthened by a great tower which dominated the whole slope. It would be difficult to form approaches, for the rock was bare of soil and afforded no cover of any kind.
Hitherto the Carthaginian generals had scrupulously respected the territory of the Saguntines, but now that the rest of Spain was subdued it was necessary to reduce this advanced post of Rome — this open door through which Rome, now mistress of the sea, could at any moment pour her legions into the heart of Spain.
The Saguntines were not ignorant of the danger which threatened them. They had again and again sent urgently to Rome to demand that a legion should be stationed there for their protection. But Rome hesitated at despatching a legion of troops to so distant a spot, where, in case of a naval reverse, they would be isolated and cut off.
Hannibal had not far to look for an excuse for an attack upon Saguntum. On the previous year, while he had been engaged in his campaign against the Carpatans, the Saguntines, taking advantage of his critical position, had made war upon the town of Torbola, an ally of Carthage. Torbola had implored the assistance of Hannibal, and he was now preparing to march against Saguntum with his whole force without waiting for the arrival of spring. His preparations had been silently made. The Saguntines, although uneasy, had no idea of any imminent danger, and the Carthaginian army collected in and around Carthagena were in entire ignorance that they were about to be called upon to take the field.