## 1 Introduction  
Landslides are one of the main natural hazards that can threaten the cultural heritage of humanity around the world [1, 2]. The monitoring of unstable slopes joined with geological, geotechnical, and geomorphological studies is necessary to evaluate the risk and to plan the mitigation strategy. Around the world, several archaeological/cultural sites were the object of landslide monitoring, for instance: Macchu Picchu in Peru [3], the Monemvasia historical site in Greece [4], and the Vardzia Byzantine monastery in Georgia [5]. In Italy, several cultural sites, potentially affected by a landslide, are monitored such as: the town of Pitigliano [6], San Leo [7], Orvieto [8], or San Fratello [9]. The choice of the best monitoring solution depends on several factors, like landslides' typology and velocity, the interaction with anthropic structures, and the available budget [10, 11, 12]. Another essential element is the purpose of the adopted solution since the structure of a monitoring system used for civil protection activities is different from a monitoring solution adopted for a periodical control of the slope evolution. For this reason, a general solution that can be selected at every site and the condition is usually challenging to define. The site-specific characteristics thus are an important element that should be considered during the definition of the monitoring network and strategy. Global navigation satellite system (GNSS) sensors are one of the well-known solutions for slope instabilities' monitoring [13]. In recent years, the advance in GNSS technology allowed for creating new low-cost sensors that can provide continuous monitoring with good precision and accuracy and limited costs [14; 15]. Nowadays, the use of low-cost solutions is commonly considered as not robust enough to support early-warning procedures. However, its deployment can be considered for permanent installations aimed at controlling the evolution of slope instability and detecting critical trends. In this context, these low-cost solutions can be regarded as a good alternative to periodical measurement campaigns. At the same time, low-cost instruments can help the installation of more precise and high-cost monitoring solutions only where and when it is necessary. As described in [16], the acquisition of monitoring data is the first essential step for the set-up of a decision-makers' support procedure for risk management. Other important elements are a correct interpretation of monitoring data and a good communication strategy that can be used to share monitoring results with decision-makers and people that can be involved in the evolution of the slope instability. Correct risk communication is nowadays considered an essential element for a proper management of emergencies [17]. In this study, we present the first outcome of a continue and near-real-time monitoring network based on low-cost GNSS on the unstable cliff that affects the part of the adjacent area of the Madonna del Sasso Sanctuary, facing the Orta lake in Piemonte region (NW Italy). The sanctuary, built in the 18 th-century, is an important cultural heritage site visited by many tourists and peregrines. The instability of the courtyard in front of the sanctuary is a factor of risk for people that visit this important cultural heritage site, but also for people that live at the base of the cliff, close to the Orta Lake. Different authors have studied the slope instability that affected the frontal part of the Sanctuary courtyard in recent years [18; 19; 20; 21; 22]. The Madonna del Sasso site is also monitored by the _Agenzia Regionale per la Protezione Ambiente_--_ARPA_ (The regional environmental protection agency of Piemonte region). In this work, the main feature of installed low-cost GNSS systems and the first outcome of the first-year monitoring are presented and discussed. We also propose a possible monitoring strategy that considers the use of semi-automatized procedures for the identification of anomalous trends.