## 2 The \"Bottini\" of Siena  
The so-called \"Bottini\" are the medieval aqueducts that still feed the most part of the historic fountains in the Centre of the City of Siena, Tuscany, Italy. They are constituted by a series of galleries dug below the centre of the city and its close neighborhoods (see Figure 1a). The whole network is around 25 km long, and is composed of two main branches named \"Bottino Maestro di Fonte Gaia\" and \"Bottino Maestro di Fontebranda\" (from the names of the two monumental fountains respectively fed by the two branches) and a large number of secondary channels of different lengths. The structure was built from the XIII to the XV century and it is still perfectly preserved in its central sections while it is affected by different levels of degradation in the peripheral portions. The dimensions of the galleries are roughly the same for the most part of the network: their cross section is characterized by a 170 cm average height and a 90 cm average width. For the most part the galleries are directly dug in the tuff stone that is present below the whole city, while some sections have been covered with bricks to prevent possible collapses. The water flows in a small open-air duct dug in the floor of the galleries: its cross section is roughly 20x8 cm and its slope is about 0.1%. While the path of the \"Bottini\" mainly runs from North to South, the galleries are not perfectly straight. indeed, they are characterized by a large number of slight curves that make the line-of-sight unachievable along the whole path. Along the way, several inscriptions (like the one shown in Figure 1b) can be found on the wall that giveprecious historical evidence about the use of the aqueduct by the noble families of the city. Nevertheless, they are at a great risk of disappearing due to the harsh environmental conditions. Indeed, the \"Bottini\" system presents very high levels of humidity, while periodic flooding occurs due to heavy rains, thus, threatening the stability of the whole structure. For this reason, a pervasive real-time monitoring infrastructure is of great importance for the maintenance of the whole structure. Due to the peculiarity of the environment, the number of parameters to be monitored can be potentially very high. These concern both air and water and include the following:  
* For air:
* Temperature and humidity;
* Currents and flows;
* Concentration of gases (with a specific focus on radon which is radioactive and present in underground environments);
* For water:
* Electrical conductivity;
* Oxidation-Reduction Potential, (ORP);
* Dissolved oxygen;
* Presence of dissolved gases;
* Concentration of Ca, Na, Mg, K, chlorides, sulfates, carbonates and organic compounds. All these parameters affect the preservation of the environment and the safety of people and, hence, should be kept under control. In particular, they should be measured in different spots along the way and collected in real time in order to allow promptly intervention in case of critical situations. Nevertheless, a high sampling rate is not necessary because all the parameters of interest are not expected to present fast variations. Ideally, a hourly sampling rate suffices the requirements. In the \"Bottini\" the electricity grid is not present nor can it be deployed. Sensing nodes should be powered by batteries and, accordingly, an important requirement is the power consumption in order to avoid frequent battery replacements. Similarly, since no wired connection is possible, a wireless data transmission infrastructure must be considered. Moreover, the connection with the surface is possible only at a limited number of spots (at the entrances): this means that, in order to cover all the structure, a wireless local area network is mandatory.