What might a Russian encirclement of Kyiv look like?
First, the Russians need to physically cut the city off on the ground. This will be an enormous undertaking.
The Russians will need to create (at least) a 90km-long cordon around the city. In normal military operations, a battalion-sized organisation (what the Russians call a battalion tactical groups, or BTG) occupies a "frontage" of about 1-2 kilometres.
Surrounding Kyiv will require a large military force — around 40-50 BTGs. This is about half of Russia's overall combat power.
They will need to cut the city off to prevent defenders and others from leaving. This will be the mission of the "inner cordon" of the Russian encirclement. The Russians will also need an "outer cordon" to prevent supplies and reinforcements getting into Kyiv. The magnitude of Russian forces required to do this means it probably isn't viable given the other requirements for combat units in the east and south.
The Russians might therefore opt for a looser cordon around Kyiv. But this would allow the Ukrainians to resupply the defenders, prolonging any siege and providing reinforcements to defend the city in the event of a Russian assault.
'Shaping operations'
At the same time the Russians will seek to cut off power to Kyiv. This will have a major impact on civilian morale. It also prevents long-term storage of perishable food.
The Russians will also attempt to destroy communications networks. This breaks down the coordination of defenders. It would also thwart their attempts to communicate with outside military forces to coordinate resupply and reinforcements.
Importantly, if the Russians destroy communications networks in Kyiv, they will stop the Ukrainian President talking to, and rallying, his people.
All of these manoeuvres are what are called "shaping operations". They are Russian activities that are required to provide a foundation for any subsequent attack on the city.
What might a Russian assault on Kyiv look like?
In short, dreadful. A Russian attack on Kyiv would seek to capture the city (and the President). Russians may not seek to hold the entire urban area. They may instead opt to only seize key nodes and portions of the city where Ukrainian politicians, government officials and the military are located.
But in undertaking a nodal approach, large segments of the city will remain in Ukrainian hands. These become urban bastions to provide logistical support from which attacks on the Russians can continue over time.
The size of Kyiv (840 square kilometres) will have a significant impact on attackers and defenders. Kyiv has tall buildings and a grid of roads both wide and narrow. Because of this, neither side will be able to concentrate large numbers of troops at any place and time. It will be a battle of thousands of small military teams against each other at very close quarters. Every building is a potential bunker, every road a potential ambush zone.
There are also extensive underground tunnels and spaces.
The Ukrainian defenders, who have out-thought and out-fought the Russians in most tactical engagements, will be able use these to great effect.
Subways and other tunnels can become safe manoeuvre corridors which the Ukrainians can use to disappear in one place and reappear in others. They can also be employed as reliable logistic supply lines and shelters for civilians.
Two critical decisions
As witnessed
in Mariupol and Kharkiv, the Russians will use massed firepower in any assault on Kyiv. There will be widespread destruction and deaths of civilians. The Russians are likely to use a combination of artillery, rockets and airdropped bombs (including cluster munitions), as well as their hugely destructive thermobaric weapons.
At some point in the defence of Kyiv, President Volodymyr Zelenskyy will have two critical decisions to make. First, how long is his presence in the city viable and when should he leave? It is unlikely his country will gain by him becoming a martyr. He may need to leave and continue leading the fight.
Second, how long should the Ukrainian military continue to defend the city? While it is the capital, with significant political value to both sides, there may be more value at some point in the Ukrainian military focusing on its self-preservation if it becomes obvious the city may fall. Neither of these are simple decisions.
There is a final risk of an attack on Kyiv. The Russians may finally conduct the kind of atrocity that forces NATO or the United States to intervene. This is not a certainty.
However, the Russians appear to have now reverted to a more brutal form of military operations which will result in large numbers of civilian casualties. The risk of further escalation in the war cannot be discounted.