The fence of Milverton's mansion, which Holmes and Watson storm, looks completely different in the evening than it does in daylight; no longer made of red brick, it is constructed from cut limestone
and is not located in Petersburg, nor even in Peterhof, but in Pitsunda, where the film crew went to shoot Swiss landscapes. After talking with the native residents of Pitsunda and its surroundings, it became clear that such a wall exists only at the ruins of the ancient fortress of Pityunt.
Two thousand years ago, on the site of the famous Abkhazian resort Pitsunda, stood the Greek city of Great Pityunt, founded by ancient Hellenes at the end of the 2nd – beginning of the 1st century BC. The area was also known as Colchis, a name that immediately recalls Odysseus and his adventures celebrated by Homer, the Golden Fleece, and the ancient Greeks’ expedition to Colchis to retrieve it. At the end of the 1st century BC, the Greeks were pushed out by the Romans, who surrounded the city perimeter with a stone wall and built watchtowers at the corners and gates.
Remnants of ancient buildings and structures have survived to this day, united in an archaeological complex. Since 1991, the ruins of ancient Pityunt have been designated the State Historical and Architectural Reserve "Great Pityunt" and hold the status of a national park-reserve. It is a true open-air museum, gathering heritage from different eras. Here you can see the ruins of the ancient Roman fortress Pityunt from the 2nd–6th centuries AD — barracks, the commander's palace, a bell tower, a chapel, an aqueduct, ancient Roman baths, and a basilica with a mosaic floor.
Also on the reserve’s territory is a temple complex from the 4th–19th centuries, including the Church of the Apostle Andrew the First-Called from the 10th century (also known as the Pitsunda Church), where organ music concerts are held. One of the monastery buildings houses the Pitsunda History Museum, which displays artifacts found during archaeological excavations.
All these structures are surrounded by a powerful stone wall from the 10th century, with a total length of 550 meters, a height of up to 8 meters, and a thickness of up to 1.5 meters. As we know, the wall in the film was also so wide and convenient that no safety measures were used during filming. The wall is made of local flagstone on a lime mortar; the masonry varies in different places: the wall was repeatedly extended and reinforced, the last time during the Turkish invasion in the 14th century. There are sections of the same height and texture as in the film, but so far it has not been possible to identify the fragments that appeared on screen.
Sources:
https://www.221b.ru/geo/3-fence3.htm
Suggested by Igor Maslennikov and Nikolay Vashchilin, found by airship
