The remnants of the wall that surrounded Beijing, China

The fortification walls, both an inner wall and an outer wall, surrounding Beijing city were built from the early 1400s to 1553.
The dimensions of the Inner city wall are:
          Length: 24 kilometers or 15 miles
          Height: 25 meters or 49 feet high
          Thickness, at ground level: 20 meters or 66 feet
                            at the top: 12 meters or 29 feet
It had nine gates.  The fortifications included gate towers, archways, watchtowers, barbicans, barbican towers, sluice gates, sluice gate towers, enemy sighting towers, corner guard towers, and a moat system.
The outer city wall had a length of 28 kilometers or 17 miles.
From 1911, after the collapse of the Qing Dynasty, the dismantling of the fortifications began.

In 1965, major deconstruction of the fortifications was commenced to allow for the construction of the 2nd wrong road, and Line 2 or the Beijing underground railway.

 In 1979, the government called off the demolition of the remaining city walls and named them cultural heritage sites. By this time, the only intact sections were the gate tower and watchtower at Zhengyangmen, the watchtower at Deshengmen, the guard tower at the southeast corner, the northern moats of the Inner city, the section of the Inner city wall south of the Beijing railway station, and a small section of Inner-city wall near Xibianmen.

For more reading, go to: https://en.wikipedia.org/wiki/Beijing_city_fortifications

As for our guide's explanation of the fortifications:

Leaving the Square to go to the Golden Mask Dynasty Show, we pass remnants of the wall that used to surround Beijing.

This wall was built in the early 15^th century and was about 24 km long, up to 15 meters high and about 20 meters thick, and had nine gates, one of which still exists today.  In 1965 most of it was removed so that the second ring road and an underground railway line could be built.

The Golden Mask Dynasty Show, Beijing, China

The Golden Mask Dynasty Show was located at the OCT Theatre in Beijing's Happy Valley. 

The theatre was quite full and the seats we had were directly behind the VIP area; as our guide told us, we had the best seats in the house. 

The play has 20 different dance scenes that depict war, royal banquets, and romance.  There are eight chapters and over 200 actors, and throughout the performance we were entertained by dancers, acrobats, costumes, lighting, and acoustics.

The story:

It is of romantic legend and historical memories, the Golden Mask Queen leads her army in defeating the invading Blue Mask King's army, and afterwards the lands return to a leisurely pastoral life until the Queen forges a 'mysterious tree'.  When the tree has grown, the Queen has a grand celebration, and releases the captured Blue soldiers, much to the admiration of the Blue Mask King.
This is followed by monstrous floods, and to save her people, and on the advice from the 'mysterious tree', the Queen sacrifices herself to save her people.  The Queen then turns into a golden sunbird flying in the sky blessing the people and that of the dynasty.

Billed as the best live show in China, described as a large scale dramatic musical, “The Golden Mask Dynasty” it lived up to its reputation and was thoroughly enjoyed by all.

It was not just singing dancing and acrobatics, it had a story and it was told so that language and cultural issues aside, it worked.  There was a narration of the story running beside the stage, but it was hard to divide attention between what was happening, and what was being related.

Then came the peacock dance, with live peacocks

And this was followed by a waterfall, well, I don't think anyone in that audience could believe what they were seeing.

I know I was both astonished and in awe of the performance.

What a way to finish off our first day in Beijing.

Oh, sorry, that high was dented slightly when we had to go back to our room.