I was listening to "The History of Rome" podcast and Mike Duncan glosses over how Scipio arrived with his army to New Carthage in Spain. New Carthage is far enough south that I would think an overland expedition would leave plenty of time to be intercepted. However it didn't sound like he came by sea because he met a naval force at the city, not traveled with one to the city.
I'm just wondering where the other Carthaginian armies were in Spain at this time. Why was New Carthage left so vulnerable and how did Scipio manage to get all the way down there?
Livy 26.19:
ad eas copias quas ex uetere exercitu Hispania habebat, quaeque a Puteolis cum C. Nerone traiectae erant, decem milia militum et mille equites adduntur, et M. Iunius Silanus propraetor adiutor ad res gerendas datus est. ita cum triginta nauium classe--omnes autem quinqueremes erant--Ostiis Tiberinis profectus praeter oram Tusci maris, Alpesque et Gallicum sinum et deinde Pyrenaei circumuectus promuntorium, Emporiis urbe Graeca--oriundi et ipsi a Phocaea sunt--copias exposuit.
To the troops which Spain had from the old army, and those which had been transported from Puteoli with Gaius Nero, ten thousand infantry and a thousand cavalry were added, and Marcus Junius Silanus, the propraetor, was sent as aid to assist. In such a way, with a fleet of thirty ships--all of which were quinquiremes--he -[Scipio, who's just received his appointment as proconsul to go to Spain] set out from the mouths of the Tiber [Ostia is both the port city at the Tiber's mouth and the mouths of the actual river itself--the one derives from the other], along the shore of the Tuscan sea, and the Gallic Gulf, and finally sailing around the promontory of the Pyrenees, he landed his troops at the Greek city of Emporiae--for they themselves are also descended from Phocaea [like the Massilians, whose city Scipio would have passed along this route--some suggest that there's a lacuna there, between the Tuscan Sea and the Gallic Gul, in which Massilia is mentioned, though my text does not mark it]
In short, he sailed from Rome and landed at the Ebro. From there he began his march southwards, with his ships following along the coast
Scipio, with his own logistical acumen, and the fleet carrying most of his supplies (but not soldiers), was able to move his soldiers very, very, quickly by the standards of pre-modern warfare. He moved 30,000 soldiers from Tarraco to New Carthage, 400 miles, in about three weeks. During the first 250 miles, which took him to the Sucro/Jucar River, he made it look like (through misinformation and route of march) that he then planned to advance inland towards the Tagus Valley to engage Hasdrubal Barca.
Instead, he marched south, and his army covered the last 150 miles in only six days, surprising both Hasdrubal and the city itself. This rate (25 mi/day) was twice the speed Hasdubal could have moved, he would have been caught flat-footed, even assuming that he found out immediately that Scipio was heading to New Carthage.
The armies of Mago Barca and Hasdrubal Gisgo were also present in Spain, but further away from New Carthage. They were not engaged with Roman forces elsewhere, as Scipio had every Roman on the peninsula with him, save a few thousand he left on the Ebro river as he marched. Rather, they were likely positioned to protect the Punic frontier in Baetica (Andalusia) as there were still many potentially hostile Iberian tribes outside of Carthage's dominion.
I literally just discussed this with my professor a few days ago, although I don't believe that his analysis appears in any published sources to cite.