The war between Ukraine and Russia has been going on for more than a year.
While Russian forces are advancing in some areas, Ukrainian forces are preparing to launch a "counter-attack" with arms support from Western countries.
Analysis of hundreds of satellite images by the BBC Verification Service has revealed Russia's defensive preparations against a possible Ukrainian attack.
Crimea, Ukraine, was illegally annexed by Russia in 2014.
Satellite images revealed Russia's defense preparations in Crimea.
The footage shows "dragon's teeth", pyramid-shaped concrete blocks designed to block tanks and military vehicles.
Behind them is a line of trenches against attacks from inside. Some bunkers can also be seen in this line.
Piles of felled trees, excavation tools and dragon's teeth show that the preparations were still underway in March, when the satellite image was taken.
Military experts say this line of defense is more of a precautionary measure than an anticipation of a naval attack from Ukraine, where Russia's naval capacity is low.
Satellite imagery from the small town of Tokmak shows two trench lines being dug in the northern part of the town where Ukraine could attack.
Behind these trenches is a three-tiered ring of fortifications surrounding the city.
Above the satellite image is an anti-tank trench, usually 2.5 meters deep and designed to stop any enemy tank that tries to cross it.
Behind the trench are the dragon's teeth and another line of trenches.
On the E105 highway connecting Russian-controlled Melitopol in the south and Ukrainian-controlled Kharkov in the north, an anti-tank handek and trench line has also been prepared.
If Ukrainian forces try to use this road, Russian defenses can target them with heavy weapons.
The Russian defense is also close to the other nearby highway T401.
Russia estimates that Ukraine is planning to retake the city of MariUpol.
In this context, the BBC Verification Service decided to look at the area surrounding the city and found circular trenches.
Located near the small village of Rivnopil, about 55 km north of Mariupol, the mounds in the center of each circular trench probably have the function of protecting artillery or stabilizing weapons.
The circular trenches, meanwhile, allow soldiers to move around to take cover and aim artillery in any direction.
Analysts point out that Ukrainian forces could detect many of these defenses using similar satellite imagery and drones