510 PADUS. ■where it separates from the main stream. Several smaller tributaries of the river in the highest part of its course are noticed in the Tabula or by the Geographer of Ravenna, which are not mentioned by any ancient author; but their names are for the most part corrupt and uncertain. Though flowing for the most part through a great plain, the Padus thus derives the great mass of its waters directly from two great mountain ranges, and the consequence is that it is always a strong, rapid, and turbid stream, and has been in all ages subject to violent inundations. (Virg. Georg. i. 481; Flin. I. c.) The whole soil of the lower valley of the Po is indeed a pure alluvial deposit, and may be con- sidered, like the valley of the Mississippi or the Delta of the Nile, as formed by the gradual accumulation of mud, sand, and gravel, brought down by the river itself and its tributary streams. But this process was for the most part long anterior to the historical period ; and there can be no doubt that this portion of Italy had already acquired very much its present character and configuration as early as the time of the first Etruscan settlements. The valley of the Padus, as well as the river itself, are well described by Polybius (the earliest extant author in whom the Roman name of Padus is found), as well as at a later period by Strabo and Pliny. (Pol. ii. 16; Strab. iv. pp. 203' 204, V. p. 212; Plin. iii. 16. s. 20.) Con- siderable changes have, however, taken place in the lower part of its course, near the Adriatic sea. Here the river forms a kind of great delta, analogous in many respects to that of the Nile; and the pheno- menon is complicated, as in that case, by the existence of great lagunes bordering the coast of the Adriatic, which are bounded by narrow strips or bars of sand, separating them from the sea, though leaving open occasional channels of communication, so that the lagunes are always salt and affected by the tides, which are more sensible in this part of tlie Adriatic than in the Mediterranean. (Strab. v. p. 212.) These lagunes, which are well described by Strabo, extended in his time from Ravenna to Altinum, both of which cities stood in the lagunes or marshes, and were built on piles, in the same manner as the mudern Veiiice. But the whole of these could not be fairly considered as belonging to the Delta of the Padus; the more northerly being formed .at tlie mouths of other rivers, the Athesis, Jleduacus, &c., which had no direct or natural communication with the great river. They all, however, comnmnicated with the Padus, and with one another, by channels or canals more or less artificial: and as this was already the case in the time of Pliny, that author distinctly reckons the mouths of the Padus to extend from Ravenna to Altinum. (Plin. I. c.) From the earliest period that this tract was occupied by a .settled people, the necessity nmst have been felt of embank- ing the various arms and channels of the river, for protection against inundation, as well as of fcon- structing artificial cuts and channels, both for car- rying off its superfluous waters and for purposes of communication. The earliest works of this kind are ascribed to the Etruscans (Plin. /. c), and from that time to the present day, they have been carried on with occasional interruptions. But in addition to these artificial changes, the river has from time to time burst its banks and forced for itself new chan- nels, or diverted the mass of its waters into those which were previously unimportant. The most re- markable of these changes which is recorded with certainty, took place in 1152, when the main stream PADUS. of the Po, which then flowed S. of Ferrara, sud- denly changed its course, and has ever since flowed about 3 miles N. of that city. Hence it is probable that all the principal modern mouths of the Po, from the Po di Goro to the Po diLevante, were in ancient times comp.aratively inconsiderable. Polybius (ii. 16) describes the Padus as having only two principal mouths, which separated at a place called Trigaboli (the site of which cannot be determined); the one of these is called by him Padna (naSda), and the other, which was the principal channel, and the one commonly navigated, he calls Olana or Holana ("OAara). This last is in all pro- bability the channel still called Po di Volano, which until the great inundation of 1152, above noticed, was still the principal mouth of the Po. The other is probably the southernmost branch of the river, which separates from the preceding at Ferrara, and is carried at the present day by a wholly artificial channel into the sea at Primaro, from whence it derives the name of Po di Primaro. Its present mouth is about 15 miles N. of Raveima; but it seems that in the days of Pliny, and probably in those of Polybius also, it discharged itself into the lagunes which then surrounded R.avenna on all sides. Pliny terms it Padusa, but gives it also the name of Fossa Augusta, from its course having been artificially regulated, and perhaps altered, by that emperor. (Plin. iii. 16. s. 20.) The same author gives us a detailed enumeration of the mouths of the Padus as they existed in his day, but from the causes of change already adverted to, it is very difiicult, if not impossible, to identify them with certainty. They were, according to him : 1. the Padusa, or Fossa Augusta, which (he adds) was previously called Messanicus : this has now wholly ceased to exist. 2. The Portus Vatreni, evidently deriving its name from being the mouth of the river Va- trenus, which flowed from Forum Cornelii, just as the Po di Primaro is at the pre.->ent day called the mouth of the Reno. This was also known as the Spinetitum Ostium, from the once celebrated city of Spina, which was situated on its banks [Spina]. It was probably the same with the modern Po di Primaro. 3. Ostium Caprasiae. 4. Sagis. 5. Vo- lane, previously called Olane : this is evidently the Olana of Polybius, and the modern Po di Volano; the two preceding cannot be identified, but must have been openings communicating with the great lagunes of Comacchio. 6. The Carbonaria, perhaps the Podi Goro. 7. Tl)e Fossio Philistina, which seems to have been an artificial canal, conveying the waters of the Tartarus, still called Tartaro, to the sea. This cannot be identified, the changes of the mouths of the river in this part being too considerable. The whole of the present delta, formed by the actual mouths of the Po (from the Po di Goro to the Po di Levante), must have been formed since the great change of 1152; its progress for some cen- turies back can be accurately traced ; and we know that it has advanced not less than 9 miles in little more than two centuries and a half, and at least 15 miles since the 12th century. Beyond this the delta belongs rather to the Adige, and Uiore northern streams than to the Po ; the next mouth being that of the main stream of the Adige itself, and just beyond it the Porto di Brondolo (the Brundulus Portus of Pliny), which at the present day is the mouth of the Brenta.*
- Much curious information concerning the delta of
