The protagonist retreats to the vicinity of the riverbank.

When he was looking for a new nesting site, the first requirement was to be close to the south bank of the river, so that he could get support in time and ensure that the road would not be cut off.

Then, the riverbank becomes the first choice.

However, the biggest difficulty in building a nest on the bank of a river is waterproofing. Due to its proximity to the water source, the newly built ant nest may be permeable, and the narrow passage of the ant nest is easy to form a siphon effect, resulting in the entire ant nest being flooded.

The phrase "a thousand miles of embankment collapses in an anthill" is not just an exaggeration and a metaphor, in fact, a small anthill will indeed cause long-term flooding in the earthen embankment, reducing the structural strength, resulting in pipe gushing and embankment bursting.

In China's 1998 devastating floods in the Yangtze River basin, ant infestation caused "pipe surges" in some of the dikes. Of course, the "ants" here are not ants, but soil termites. Termite-infested river embankments often appear intact on the outside, but are likely to have been severely damaged on the inside. At that time, the small jeep speeding on the Jingjiang embankment actually fell into the earthen dam, and it was even more common for pedestrians and buffaloes to fall into the "trap" in the dam.

For ants, once the nest located on the bank of the river enters the water, it is often the end of the group.

The protagonist has never lived in Waterfront City, and he doesn't know how much the river level can be raised during the rainy season. Even if you ask the original defenders of "Waterfront City", due to the annual war, they know the hydrological situation of the previous year, and they do not have long-term data.

The protagonist is unable to determine the highest water level of the Great River. So the reliable way to build a new nest is to find the main nest at a high place as much as possible and do a good job of drainage facilities.

After searching the riverbank, the protagonist quickly identifies the most suitable spot - under the huge trees he had looked at before.

Previously, when the protagonist first landed on the north bank of the river, he looked out at the nearby terrain from this tree more than 20 meters high. Now it seems that the land beneath this tree is also a suitable nesting site.

Since the leaves have been lost in winter, the protagonist does not tell what kind of tree this tree is for a while, only that its bark is dark gray, with longitudinal cracks, and peels off in patches. When it sprouts, blooms, and bears fruit next year, the protagonist will be able to identify its species.

The tree is about twenty meters tall and about half a meter in diameter at the base, and the tree is tall and straight. At the roots of the trees, the soil at the roots of the trees is more than half a meter above the nearby ground and nearly one meter above the current ice surface due to the fixation of the roots and the erosion of the river water on the area where the remaining roots have not covered.

The protagonist is interested in this half-meter and one-meter drop. The river is currently in dry season in winter, and it is about a meter from the mound under the trees. Even during the rainy season, the protagonist thinks that this height is enough to prevent floods.

There is also the inconvenience that the new nest needs to be as shallow as possible, and then expand horizontally to avoid water seepage from the lower places. But compared to other advantages, this inconvenience is tolerable.

Due to its proximity to the riverbank, it is easier for new nests to be supported from the rear. It is far away from the enemy's daily activities, and can also be undetectable during early nesting, allowing for more time for construction.

Most importantly, the terrain avoids being completely surrounded by enemies, at least on the riverside side. If you take a good look at the communication routes with the south bank of the river, the enemy will not be able to cut off the communication line between the new nest and the "waterfront city".

Between the new nest and the "waterfront city", the protagonist originally planned to build a pontoon bridge.

A pontoon bridge refers to a bridge that replaces the piers with a boat or pontoon tank and floats on the water. The military pontoon bridge assembled by the army with standard equipment is called the boat bridge. In ancient times, pontoon bridges were mostly made by laying wooden planks on top of parallel boats, rafts or ropes.

Pontoon bridges can be used for cross-river traffic. Because of its simple structure and easy erection and dismantling, it was often used as the main means of transportation in rivers and even straits in ancient times when the bridge construction technology was backward.

The history of building pontoon bridges in our country is very long, in the 8th century B.C., it was recorded that King Wen of Zhou in the Zhou Dynasty set up a pontoon bridge on the Weishui River in order to marry his wife, it has been 3,000 years since today, and it is the earliest record of building pontoon bridges. According to research, the pontoon bridge was a rare thing at that time, and the Zhou Dynasty ritual system stipulated that only the "Son of Heaven" could use it, and it should be removed immediately after use. During the Warring States Period, "etiquette collapsed", and the rules that only allowed the "Son of Heaven" to go on the pontoon bridge also collapsed.

By the Han and Tang dynasties, the use of pontoon bridges in China became more and more common. It is difficult to count the pontoon bridges that have been built over thousands of years. In many areas, pontoon bridges are built before permanent bridges are built, so that they can explore and understand the water conditions, and then seek a suitable permanent bridge type. According to rough statistics, nearly 20 large pontoon bridges have been erected on the Yangtze River and the Yellow River alone, most of which are military pontoon bridges.

For example, in the Spring and Autumn Period of 541 B.C., Qin Jinggong's mother and younger brother Zizhen were afraid of being killed by Qin Jinggong because of their own excessive wealth, and set up a pontoon bridge on the Yellow River near Linjin in Shanxi Province today, and fled to the Jin Kingdom from present-day Shaanxi with the wealth of "car weight and thousands of times", which can be described as the first Yellow River bridge.

The first Yangtze River pontoon bridge was built in the eleventh year of Jianwu (35 AD) Emperor Guangwu of the Eastern Han Dynasty in the battle with the Sichuan separatist force Gongsun Shu, Gongsun Shu had been between Jingmen, Yidu County, Hubei Province and Huya, Yichang County, taking advantage of the dangerous terrain, to erect a pontoon bridge, that is, Jiangguan pontoon bridge, in order to cut off the water traffic of Emperor Guangwu of the Han Dynasty. Later, it was set on fire by the sailors of Emperor Guangwu of the Han Dynasty using the wind.

In the first year of the Sui Dynasty (605 AD), the Tianjin Bridge was built on the Luoshui River in Luoyang, Henan, and was the first pontoon bridge built with iron chains to connect ships. Li Shimin, Taizong of the Tang Dynasty, wrote a poem, four of which are "temporarily low and frightening, but also high value waves, the water shakes the crane, and the cable turns to the brocade flowers", which is used to describe the scene of the crane on the bow of the boat that is good at fighting the wind and waves and the brocade flowers on the cable when he crosses the pontoon bridge in the royal car.

In 974 A.D., during the period of Song Taizu, the second pontoon bridge was erected at the quarry rock in Dangtu County, Anhui Province in the middle and lower reaches of the Yangtze River, which provided important support for the Song soldiers to destroy the Southern Tang Dynasty, unify the whole country, and march to the south of the Yangtze River.

During the reign of Yuan Shizu, in order to unify the southwest region and send troops into Sichuan, more than 20 military pontoon bridges were erected on the Baima River, Hejiang, Peijiang River, Qingjiang and other rapids, and these pontoon bridges made great contributions to Kublai Khan's unification of the southwest.

The earliest pontoon bridge in the West was written by the ancient Greek historian Herodotus: the Persian king Darius built a pontoon bridge on the Bosphorus when he invaded Greece. Unlike China's pontoon bridges, which are mostly used to cross rivers, pontoon bridges here are built for floating sea.

The pontoon bridge has a long history and works very well, but the protagonist is somewhat not satisfied.