The northern boundary of the proper Tuscan territory was formed by the Arnus; the region north from the Arnus as far as the mouth of the Macra and the Apennines was a debateable border land in the possession sometimes of Ligurians, sometimes of Etruscans, and for this reason larger settlements were not successful there.
The southern boundary was probably formed at first by the Ciminian Forest, a chain of hills south of Viterbo, and at a later period by the Tiber.

We have already( 6) noticed the fact that the territory between the Ciminian range and the Tiber with the towns of Sutrium, Nepete, Falerii, Veii, and Caere appears not to have been taken possession of by the Etruscans till a period considerably later than the more northern districts, possibly not earlier than in the second century of Rome, and that the original Italian population must have maintained its ground in this region, especially in Falerii, although in a relation of dependence.
Relations of the Etruscans to Latium From the time at which the river Tiber became the line of demarcation between Etruria on the one side and Umbria and Latium on the other, peaceful relations probably upon the whole prevailed in that quarter, and no essential change seems to have taken place in the boundary line, at least so far as concerned the Latin frontier.

Vividly as the Romans were impressed by the feeling that the Etruscan was a foreigner, while the Latin was their countryman, they yet seem to have stood in much less fear of attack or of danger from the right bank of the river than, for example, from their kinsmen in Gabii and Alba; and this was natural, for they were protected in that direction not merely by the broad stream which formed a natural boundary, but also by the circumstance, so momentous in its bearing on the mercantile and political development of Rome, that none of the more powerful Etruscan towns lay immediately on the river, as did Rome on the Latin bank.

The Veientes were the nearest to the Tiber, and it was with them that Rome and Latium came most frequently into serious conflict, especially for the possession of Fidenae, which served the Veientes as a sort of -tete de pont- on the left bank just as the Janiculum served the Romans on the right, and which was sometimes in the hands of the Latins, sometimes in those of the Etruscans.

The relations of Rome with the somewhat more distant Caere were on the whole far more peaceful and friendly than those which we usually find subsisting between neighbours in early times.