## 1 Introduction
### The History of the Inca Trail and the Bridges in the Territory of Peru  
As mentioned above, many of the ancient cultures that inhabited the territory of Peru in its beginnings learned to live in harmony with the ecosystem, where a broad and comprehensive learning of the territory was evident [5; 6]. This is how, for example, the Inca culture learned from the Andean territory by making use of its natural resources without the purpose of exploiting them but rather by making harmonious and sustainable use of them, as well as avoiding the risks of disasters due to extreme hydrometeorological events. In this way, construction in areas with high levels of exposure was avoided, thus reducing the vulnerability of human settlement systems to climatic threats. It is also worth noting that housing structures were designed and built to resist the effects of large earthquakes, thus avoiding their collapse [7]. It was in this context that the Inca Empire sought to expand into the Andean region, where, through an extensive network of roads, it managed to reach as far north as the current southern territory of Colombia, the city of Quito in Ecuador, Peru, Bolivia, Jujuy in Argentina, and as far south as the El Maule region in Chile. The roads built by the Incas were based on earthworks and cobblestone structures, which allowed people called Chasquis to travel through various territories, connect different communities, and move in different types of climates, given the ecological diversity of the Inca Empire. This road allowed people to connect where there were important rivers, and thus, the Incas learned to build bridge structures. The Inca trail, also called Qhapaq Nan (Qhapaq meaning big and Nan meaning road in the Quechua language), was built without the use of metal or iron, the wheel, or draft animals and covered 40,000 km throughout the Tawantinsuyu (Inca Empire) [8]. Sophisticated constructions could be seen on the Inca trail: flat and stepped cobblestone roads, reservoirs, food and supply depots, as well as watchtowers and fortifications. The road network allowed the Inca to supervise and administer a large Andean territory, crossing one of the most extreme physical geographies on the planet, from mountains with snow-covered peaks of 6768 m above sea level (Huascaran Mountain), passing through jungles, grasslands, and deserts [9]. Inca engineers understood the hydraulic and hydrological behavior of water flow, the action of gravity, and wind erosion, thus optimizing road design for human and animal pedestrian traffic with camelids. An estimated 6% of the Inca trail network is still visible, and existing roads are still used and maintained by Andean indigenous communities today. Currently, these roads are being studied to understand Inca engineering techniques and their application to contemporary projects. Monumental architecture, terraced agriculture, sophisticated water management infrastructure, food storage, the domestication of high Andean camelids, and the domestication of thousands of potatoes and hundreds of varieties of quinoa and corn are some of the other amazing achievements of the Inca culture. Today, Andean indigenous communities are proud of their heritage and still live sustainably and in balance with the natural environment [3]. Among the technical solutions used to overcome a landscape as rugged as the Andes Mountain range, one of the most interesting is bridges, which were used to cross water courses or to climb ravines and thus shorten journeys. These were built with various engineering techniques and made of various materials such as stone, wood, and plant fiber [10; 11; 12].