Trenches
As no one expected the war to last as long as it did, the first trenches were hurriedly made. They were holes dug by soldiers to protect themselves from the enemy. With modern weapons, even a shallow hole could sufficiently protect soldiers from the enemy. However, these hastily constructed defenses often flooded and collapsed. As the front line stabilised, these trenches became deeper and more elaborately made.
Construction
Trench construction was difficult. According to the British trench guidelines, it took nearly six hours for 450 men to construct 250 meters of trench. After this they would have to add the other materials necessary: barbed wire, board walks, and sand bags, for example. There were three main ways of constructing trenches: entrenching, sapping, and tunneling. Entrenching is the "normal" method of digging that you and I would use: standing on the ground, and digging downwards. This method was most efficient, as it allowed for many men to construct a trench at once. However, it also left the men exposed to the enemy above ground. Sapping involved digging at the ends of the trench inwards. Only a few men could do this at a time. Tunneling is exactly as it sounds like: it is like sapping, but leaving ground overhead that would later be removed.
Layout
A trench was generally around two meters deep and two meters wide, the trenchlines were never built in straight lines. Typically, trenches zig-zagged, as this prevented infiltrating enemy troops from simply firing down the length of the trench lines, and it helped prevent any gas attacks from spreading far down the line.
Armies typically built three lines of trenches. The first trench, and the namesake for this site, was the front line. This was the trench closest to No Man's Land (the territory controlled by neither side of a battle), and the most dangerous. The front line was connected to communication trenches to move supplies, equipment, and men forward, without exposure. The second line, typically around 75 meters back, was the support trench, a sort of back-up for the front line. If the enemy has successfully occupied the first trench, the support trench would be occupied instead. Another 300 meters back, the third trench was the reserve trench. Here, the reserve troops could amass for a counter-attack, if the first two trenches were occupied.
Health
The trenches of World War One were decidedly unhygienic. Pests roamed around the land, including giant rats that I'll describe in the next section. Men could not wash themselves in the trenches: they had limited access to running water, and often did not have the time to think about hygiene. The toilets of the trenches were usually just large buckets in a side trench, but they were not always used. Using the toilet left you vulnerable to enemy attack, and some soldiers would opt to relieve themselves where they were. Understandably, dysentery was a common ailment in the trenches. Dead bodies littered the land, and continuous gunfire was heard all around. This gunfire was enough to drive anyone mad, and, indeed, many were driven mad during the Great War.
Rats and Pests
In the cramped trenches, many parasites thrived. The worst of these were the rodents: rats gorged themselves on human remains, and grew to massive sizes: some reported rats as big as domestic cats. The rats would also sometimes eat the fresh rations of the soldiers, and nibble at the soldiers themselves as they slept or if they were wounded. The rodents would attack a corpse's eyes, and then burrow themselves into the bodies. They were a terrible problem: as one pair of rats can produce as much as 880 offspring a year, the trenches were soon crawling with millions of them. Some men made pets of the animals as company, but most rats were fearsome creatures.
Another terrible pest of the trenches were lice. Lice as you probably know, are parasites that are hard to get rid of; they bred in uniforms and caused the soldiers to itch. Although this was not know until 1918, lice were also the cause of the dreaded Trench Fever, a painful disease that began as severe pain and a high fever. This disease was caused by the bacterium Bartonella quintana, which the lice spread. Many soldiers succumbed to the disease, and only twelve weeks of recovery away from the trenches would cure it. Other pests of the trenches included frogs, slugs, and horned beetles. Normally, they were not problems, but if you happened to slip on a frog and fall, it could be deadly!
Weather Conditions
Another terrible aspect of the trenches were the weather conditions. Most trenches were muddy, cold, and overall depressing. Many soldiers simply died from exposure to the cold, as the temperature within a trench was often below zero in the winter. Soldiers would lose fingers and toes to frostbite, and trenches were often filled by the rain— sometimes, the trenches would fill with water up to the soldiers' waists. This submersion caused a terrible fungal infection called "Trench Foot." The feet that succumbed to this could turn gangrenous, and often needed to be amputated. As conditions improved, Trench Foot became less frequent; however, a trickle of cases continued. Good socks and boots were essential to some soldiers.
Burials
Often, burials did not happen at all for the dead. Death was a constant companion of the soldiers, and they had no time to bury the multitudes of corpses. Bodies would lie in No Man's Land for ages, and even when the front line moved forward, these bodies were sometimes not buried, and often could not be identified. Soldiers would first bury their known companions, then their fellow countrymen, and then finally the enemy— but they rarely buried the enemy. On some battlefields, bodies were not buried until after the war. (Thanks to Jordan M. for alerting me to the typo in this section!)
For More Information
My drawings do not accurately reflect how horrible the trenches could be. Try looking at photography taken of the trenches, such as this photo gallery from First World War.com, these haunting photographs from the World War I Document Archive, or these amazing colour photos from World War I.