**4. Discussion**

The study here presented about the SE area of Ceggia, where several buried traces, potentially interesting from a geological and archaeological point of view, have been identified by aerial and satellite images, demonstrated the high value of the multidisciplinary approach to understanding, in similar contexts, the evolution of a territory.

In particular, the multitemporal combined analysis of aerial images and historical cartography of Ceggia demonstrated that the linear systems visible in the aerial photos (Figure 1) do not pertain to the modern reclamation (end of the 19th and 20th centuries), and it is not previously documented by the available historical cartography (until the middle of the 16th century), which represent only the marshes in the area. The same analysis highlighted that the artificial section of the Piavon, realized between the end of the 16th and the beginning of the 17th century, cuts this relict system, suggesting its earlier existence.

On the contrary of the hypothesis of Dorigo [15], therefore, these lines evident on the field cannot be attributable to possible interventions made during the Republic of Venice in the second half of the sixteenth century. The evidence collected in this study, thanks to the sporadic fragments of Renaissance material found along the exposed section in the analyzed drainage channel, demonstrates that the area has been undoubtedly frequented in that period but, most probably, only for hunting, fishing, and to provide natural materials.

It can, therefore, be assumed that the system visible in the photos is older than the 16th century and probably even older than the 14th century, considering two different Medieval documents [15,60] which describe the area occupied by marshes.

The preliminary information made by the multi-temporal analysis described before is then completed and validated by the new data provided by the field non-direct and direct measurements.

Starting from the buried anomalies visible in the aerial photos, the geophysical FDEM and ERT acquisitions better defined the localization and spatial relation among these different structures, driving for the sample core positioning. The geophysical data also integrated the information about the system in-depth, only partially directly investigated by the exposed section and the sample cores.

The buried soil at about 2 m depth in the central part of the stratigraphic cross-section (Figures 7 and 8) indicates the existence of a major depositional hiatus in the alluvial succession, probably related to the so-called post-Last Glacial Maximum (post-LGM) unconformity, well known in the whole Venetian-Friulian plain (e.g., [61–65]). This unconformity is associated with soil formation in the interfluves (the "caranto palaeosoil") and the development of incised valleys along with the concentrated streamflow, as a dynamic reaction of the fluvial system to the deglaciation of the mountain catchments at the end of the LGM. In this framework, the tabular sandy body below the buried soil is attributed to the LGM aggradation of the alluvial plain. The two clay lenses at the SW and NE extremes of the cross-section should represent the top portion of the infilling of post-LGM incised valleys of the Piave River, whose existence has already been reported in this distal sector of the Piave megafan (e.g., [4,66]).

The overlying tabular silty-clay layers were probably deposited by eastern branches of the Piave River before Roman times and after the 2nd millennium BC (Piavon Unit in [4]). The topmost, thin layer of gray mud deposits preserved under the plough horizon in the SW extreme of the section (i.e., US 109) probably corresponds to the so-called Ceggia unit, a thin (<2 m) sedimentary unit that was deposited in fresh-water coastal swamps during the Holocene up to modern times on wide areas of the Piave coastal plain [4]. The preservation of these deposits in the study area was probably possible thanks to the fact that its deposition took place in a depression that, in turn, was created by the higher subsidence in the organic clay fill of the incised valley in respect to the nearby interfluve (a common process in the Venetian plain, e.g., [67]). The sinuous paleochannel evident in aerial photographs is probably related to local drainage along with this elongated depression, that is used to follow the buried Holocene incised valley and debouched in the Canalat just upstream of the Roman bridge (Figure 4).

The core samples and the exposed section have, therefore, highlighted that the paleochannel visible in the aerial photos is more recent than the Roman bridge, on the contrary to as hypothesized in previous studies [68]. These data, therefore, exclude that this river branch flowed in the Roman age, at the same time making possible a hydraulic-agricultural arrangemen<sup>t</sup> of the area at that time. In this hypothetical scenario, the river that crossed the area flowing below the *Annia* three-arched bridge probably corresponds to the current Canalat. This hypothesis can be proved by the large amount of Roman archaeological materials found along the channel (Figure 4b) and by the remains of the Roman villa just close to it. The characteristics and geometry of sediments corresponding to the dark linear traces allow their interpretation as the infilling of couples of artificial ditches running in pairs and converging perpendicularly at the junction. The time window bracketed by the radiocarbon date spans from the beginning of the 4th century to the first half of the 2nd century BC. This confirms that the ditches are not medieval, nor modern. Considering the possibility that the dated wood pertained to a large timber of mature age, this date is not in contrast with the deforestation and installation of a pre-Roman route before the building of the *Via Annia*, attributed to the second half of the 2nd century BC, possibly as early as 153 BC [5,6]. If we take into account, moreover, that from the photos of the GAI 1954 flight, one of the axes with WNW-ESE trend delimited by these ditches seems to detach from the *Annia* at the height of the site occupied by the military base, then we have another good reason to assume that the system dates back to a phase in which the road layout was evident on the surface and possibly in use.

More scant is the subsurface evidence of the road that supposedly runs in between each pair of ditches. The relative sediments have probably been largely beheaded by ploughing and other modern agricultural activities. The US 104 is a possible remain of the lower foundation of the road; nevertheless, considering known examples of the *Via Annia* road investigated in archeological excavation (e.g., Ca' Tron Michelini; Vigoni [6]), it has to be considered that even such a major consular road outside the main cities was just a dirt road, with faint archaeological evidence. Examples of similar structures have been highlighted in Villadose in the *ager Atrianus* [69–71], but also in the territory north of Padua [72], in the Altinate [72], and in the Valli Grandi Veronesi [69,73]. If we consider, in fact, the hydraulic instability of the sector, it is likely that a system of roads on elevated embankments and ditches like the one found was the most obvious solution to be adopted to ensure the drainage of water from the fields as well as access to the area even in periods when water stagnation could still occur. Moreover, it is not to be excluded that, in Roman times, these banks were also used for seasonal grazing of sheep, in relation to the phenomenon of transhumance, which involved the wintering of flocks coming from mountain areas in the coastal plains. This practice, found in various areas of the Roman Veneto, is well documented, especially in the nearby Altinate territory [74]. Regardless of the use to which the accommodation could have been put, it should be pointed out that the mesh of the buried evidence is not perfectly orthogonal, and the surface of the plots cannot be traced back to the Roman actus. Such a finding, combined with the location of the Roman sites along the river Canalat, leads us to hypothesize that these spaces were not organized according to a centurial model, although they were equipped with hydraulic arrangements that probably guaranteed their seasonal exploitation [75,76].

As it has been pointed out for the plain of Lugo [77], during the Roman Republic, several areas exposed to hydrogeological risk were not regularly divided for the agricultural practices, probably due to the environmental constrains (e.g., presence of swamps or ponds). The conditioning by the environmental context, in terms of population and territorial structure, is also underlined by another recent study which, analyzing the southern centuriated landscape of Padua, focuses on the undefined eastern limit of the agro (coinciding with the coastline of the Roman age), assuming the presence of settlements and cultivated areas also in the area of coastal marshes mentioned by ancient authors [78].

Finally, it is not to be excluded, even if it seems less probable, that the important layout given by the Romans in the area of Ceggia, after a phase of abandonment, was restored and readapted in the Early Middle Ages, losing its original shape. If the arrangemen<sup>t</sup> of the sector was, therefore, to be traced back to the Roman age, as the data examined so far would seem to suggest, its progressive defunctionalisation could instead be attributed to changed environmental and land-management conditions.

There are some signs of a worsening of the state of the coastal areas of the upper-Adriatic lagoon area, already from the 3rd–4th centuries AD, when the action was taken on the *Annia* to restore some stretches of the route ruined by the marshy waters [7]. However, it is from about the middle of the VI century AD, as suggested by the chronicle of Paul the Deacon [79], that a phase of strong hydraulic instability [80], characterized by alluvial phenomena and the swamping of vast portions of territory previously inhabited [1,81], seems to have begun.

This important environmental change, which perhaps led to the deterioration of the Roman land system, had to be favored by the concomitant rarefaction of the settlement typical of the Late Antique-Early Medieval period, as well as by the lack of both maintenance and capillary water control.

On the basis of the picture outlined, it is therefore not to be excluded that the failure to find medieval material on the surface in the SE area of Ceggia is to be associated precisely with this settlement decline, due to the establishment of new socio-political and economic balances and the occurrence of climatic and environmental changes mentioned above.

If we listen to the sources, it is likely that the area of Ceggia and those close to the settlement of *Civitas Nova*/*Heraclia*, were already a ffected at the time by marshy and wooded environments and uncultivated areas for pastoral and breeding activities [82]. The natural modifications occurred during the time provide the image of a variegated landscape, without the man intervention except in an occasional and unsystematic manner. It is di fficult, therefore, to think that in such a context, it has been possible to create a system like the one object of this study.
