On Monday, a satellite spied a 40 mile-long column of Russian tanks. It was heading for KyivThe capital of Ukraine.. The convoy could "lay siege to the city".

This has not happened. The Russian advance has stalled. Putin's forces have become easy targets for Ukrainian soldiers.

Why? Food shortages. And too much mud.

Tank tires need to be in peak condition to mow through soft surfaces. As military vehicle expert Trent Telenko says: "When you leave military truck tires in one place for months on end, the side walls get rotted." Air leaks out. Insects build nests. Sunlight causes them to become brittle. 

The tyres must be turned over and moved regularly. The Russian tanks have remained still for some time, and are now not functioning properly. The moment they encounter mud, they begin to get stuck.

There is currently a lot of mud in Ukraine. The country is entering the spring RasputitsaA Russian phrase meaning "time without roads". The Rapustitsa occurs each year in spring and autumn and lasts about a month and a half..

Military vehicles and mud have long been enemies. The first tanks used by the British Army in World War One were not a success. The Battle of Passchendaele became a tank graveyard as the heavy vehicles sank into the slurry. 

Tanks began to show their mettleStrength of spirit.  in World War Two. They have become a symbol of horrific violence. When the Soviet Union wanted to stop reform in the Eastern Bloc, it sent tanks rolling into Budapest and Prague to terrify protestors. Yet they become virtually useless in mud. 

Is mud a great peacemaker? 

History is littered with examples of armies defeated by terrain. Ecologist Richard Bardgett writes: "In war, the earth matters."

In the 13th Century, NovgorodA city in Western Russia, now known as Veliky Novgorod. It was the first capital of the Kievan Rus'. It was eventually conquered by Moscow. was saved from Mongol conquest by the muddy conditions. When Napoleon attempted to invade Russia in 1812, around 180,000 members of his Grande Armee died as a result of poor weather conditions.

Others point out that mud could hamper Ukrainian efforts too. The battlefield bogs of World War One took lives on both sides. One frontline newspaper headline said: "Hell is not fire, that would not be the ultimate in suffering. Hell is mud."

And some believe it is unlikely the mud will detain Putin for long. The Soviet Union initially faltered in the freezing cold of the Winter WarAlso known as the First Soviet-Finnish War. A brief, bloody conflict between 1939 - 40 between Finland and the Soviet Union.. When the ice thawed, they adapted their tactics and quickly won.

Yes: If the world sees the Russian Army being picked off while stuck in the mud, Putin will be humiliated. It might force him to abandon his invasion in face of lasting, determined resistance.

No: Putin's convoy is just one part of his mighty war machine. Even if the mud stalls it, Ukraine will still suffer from attacks on other fronts and from the air. The best it can do is slow things down.

Or... Mud is fickle. It can hinder the Russian advance, but it can also make it difficult for Ukraine to manoeuvre around it. And if the invasion continues long enough, the soil will eventually harden.

Kyiv - The capital of Ukraine.

Rasputitsa - A Russian phrase meaning "time without roads". The Rapustitsa occurs each year in spring and autumn and lasts about a month and a half.

Mettle - Strength of spirit. 

Novgorod - A city in Western Russia, now known as Veliky Novgorod. It was the first capital of the Kievan Rus'. It was eventually conquered by Moscow.

Winter War - Also known as the First Soviet-Finnish War. A brief, bloody conflict between 1939 - 40 between Finland and the Soviet Union.