# Investigations on an Ancient Mortar from Ulpia Traiana Sarmizegetusa Archaeological Site, Romania
## 4 Discussion  
The integration of the results from Sections 3.1-3.6 involves two directions: firstly, the material characterization and the ageing processes undergone, and secondly, to what extent  
Figure 18: Histogram obtained by applying the R_combine function of OxCal Program [29]. the information confirms carbonation during hardening or if secondary/subsequent recrystallization has taken place over time, leading to rejuvenation. When S2 pyrogenic calcite and S3 C-S-H carbonation mechanisms overlap, as is the case, it cannot be a matter of rejuvenation but of a delay in the mortar hardening. Calcium carbonate in lumps was not formed exclusively by the S2 pyrogenic calcite mechanism, from the excess of slaked lime, but also by carbonation into the 'nested' hydrated forms of calcium silicates/aluminosilicates (mechanism S3). If C-S-H are present and then it is a hydraulic mortar, there are high chances that the carbonation process took a long time, making the radiocarbon date unreliable. Such assumptions on the presence/absence of possible geological calcium carbonate, unreacted lime lumps, as well a tendency of calcium carbonate to dissolve and reprecipitate with younger environmental carbon can be verified later using high-resolution instrumentation such as cathodoluminescence (CL) [33]. Also, optically stimulated luminescence (OSL) can be used to verify the correct choice of datable submicronic fractions [52]. Radiocarbon dating places the use of this mortar in the Medieval times (Middle Ages, 7-9 th centuries, more precisely), which is several centuries after [PERSON]'s withdrawal from the Dacian provinces (271-272 AD). If the radiocarbon date of the mortar taken from the plinth of the central statue in Forum Vetus had coincided with the time of its erection, i.e., 2 nd century AD, the research would have been limited to characterizing the material (and obtaining a possible manufacturing formulation). In fact, the exact moment of construction is unknown but, the [PERSON]'s forum was finished, according to an inscription, around 110 AD [53]. In the following period, a series of interventions were carried out in Forum Vetus, with the replacement of the cover limestone with marble, but there is no record of any work on [PERSON]'s statue. After 153 AD, it was extended by Forum Novum [54]. The year 255 AD marks the retreat of the Huns with the abandonment and degradation of the colony. Thus, the construction of the plinth of the statue initially attributed to [PERSON] can be included in this period of approx. 150 years. The difference of centuries compared to the radiocarbon date, given that there were no modern interventions on this architectural element until now, raises new challenges, both technical and historical. If the age is correctly represented by the radiocarbon date, there are two hypotheses: (i) a temporarily return of the Romans in the site, in which case the mortar is a Roman mortar, made with pozzolanic materials transported from the Italic Peninsula; (ii) resident craftsmen, either indigenous or migratory, possessed the knowledge and skills to develop lime mortars with locally available materials as in the case of basilica Torre de Palma [3]. Both hypotheses should be treated with caution, as there is not yet available evidence of any kind to support them. If the age is 'apparent', beyond the threshold of 100-200 years generally accepted by the literature, the phenomenon of rejuvenation/delaying of the mortar hardening must be taken into account.