You may have never heard of the Kingdom of Mercia. That's because it hasn't existed for over a thousand years. Mercia was once a great kingdom before England was a united country. The Midlands area of England is still occasionally referred to as Mercia.
The name of Mercia means "the people of the border", because the Mercians were the Anglo-Saxons along the border with what is now called Wales.
There was an era before England was united that was called "The Mercian Supremacy", because Mercia was predominant among the other pre-England kingdoms.
I am actually a Mercian. My parents told me about Mercia when I was a young boy. "Today this is England but it was once Mercia".
The following image, from the Wikipedia article "Mercia", shows the boundaries of Mercia. It is approximately what is today called the Midlands. The blue dot is where I was born and the yellow dot is the city of Birmingham. The green area was the area under Mercian influence when it's power was at it's height, basically all of southern England.
The name of Mercia is still seen and the Midlands are occasionally referred to as Mercia. Three images from Google Street View.
Mercia had a great king, called Offa. The red line in the above map is Offa's Dyke. This was a defensive ditch and berm that was dug along the border with Powys, which is now known as Wales. Not much remains of it after so many centuries but it is still visible in places. There is a walking and biking path that runs all along the route. Image from the Wikipedia article "Offa's Dyke".
There was also a great queen, called Aethelflaed, image from the Wikipedia article by that name.
The town of Tamworth proclaims itself as "The Ancient Capital of Mercia". Image from Google Street View.
In Tamworth there are two statues of Aethelflaed. Two images from Google Street View. Tamworth Castle is in the background of the first image. Kings of Mercia lived there but it might not look like it did then.
The following image, from the Wikipedia article "Mercia" is considered as the "flag" of Mercia although it wouldn't have been flying from a flagpole as we do today.
The religious center of Mercia was Lichfield. It is next to Tamworth and both are close to what is now Birmingham. Chad of Mercia is credited with helping to bring Christianity to Mercia, and was it's Bishop. Lichfield Cathedral is on the site where a cathedral was first consecrated in the days of Mercia. The following two images from Google Street View show the present cathedral and statue of St. Chad.
There are two shrines containing bones of St. Chad. One is in Lichfield Cathedral. Image from Google Street View.
The other is in St. Chad's Cathedral in nearby Birmingham. Image from Google Street View.
Aethelflaed ruled during a time of conflict and, on an expedition to the north, her forces retrieved the bones of St. Oswald. This had been an earlier king and martyr. Aethelflaed founded St. Oswald's Priory, in Gloucester, and had the bones buried there. Aethelflaed was later buried there herself.
St. Oswald's Priory is adjacent to what is now Gloucester Cathedral. It became a pilgrimage site and was certainly a factor in getting the cathedral founded nearby. This is not far from where I was born.
The following three images, from Google Street View, are what remains of St. Oswald's Priory today, although these walls were not there at the time of Mercia. The priory was damaged during the Seventeenth Century civil war.
Tamworth and Lichfield are both near Birmingham but the city of Birmingham was not there then. It is mostly a product of the Industrial Revolution and was far in the distant future at the time of Mercia.
Seafaring has been very important to Britain from the beginning and all of it's major cities are on or near the coast. Birmingham is the one exception. It is by far the largest city in the country that is nowhere near the coast. I wonder how this came to be.
What you may notice about the map above is that Mercia had very little coastline. But yet it was a great kingdom with a great influence. History is a very powerful force and my conclusion is that a major city grew up next to the Ancient Capital of Mercia, and also it's religious center, as the modern heir of Mercia, although I have never seen Birmingham associated with Mercia. This is why Birmingham breaks the apparently logical rule that a major city, in a country like Britain where everything is within 110 km of a coast, should be on a coast.
In the same way, Britain's other Industrial Revolution cities are reenactments of long-ago kingdoms. Cardiff, Newport and, Swansea are reenactments of Powys, which preceded Wales. Liverpool and Manchester are reenactments of Northumbria. Glasgow is a reenactment of the medieval Kingdom of Strathclyde.