What Schliemann actually found as he excavated the hill of Hisarlik somewhat haphazardly were contexts in the soil parallel to the contexts of geologic layers in rock.
Exposed rock displays layers of a similar composition and fossil content within a layer discontinuous with other layers above and below it.
The layer represents an accumulation of detritus over a continuous time, different from the times of the other layers.

Similarly Schliemann found layers of distinctive soil each containing more or less distinctive artifacts differing often markedly from other layers.
He had no ready explanation for the discontinuity between layers, such as "destruction," although this interpretation has sometimes been applied.
Presumably "destruction" is to be interpreted to mean some sort of malicious event perpetrated by humans or a natural disaster, such as an earthquake.
In most cases no such disaster can be proved.
On the contrary, the "many layers illustrate the gradual development of civilization in northwestern Asia Minor."

The discontinuities of culture in different layers might be explained in a number of ways.
A settlement might have been abandoned for peaceful reasons, or it might have undergone a renovation phase.
These are hypotheses that must be ruled in or ruled out by evidence, or simply be left unruled until evidence should be discovered.

What Schliemann found is that the area now called "the citadel" or "the upper city" was apparently placed on virgin soil.
It was protected by fortifications right from the start.
The layering effect was caused in part by the placement of new fortifications and new houses over the old.
Schliemann called these fortified enclosures "cities" (rightly or wrongly).
In his mind the site was composed of successive cities.
Like everyone else, he speculated whether a new city represented a different population, and what its relationship to the old was.
He numbered the cities I, II, etc.,
I being on the bottom.
Subsequent archaeologists turned the "cities" into layers (rightly or wrongly), named according to the new archaeological naming conventions then being developed.

The layers of ruins in the citadel at Hisarlik are numbered Troy I – Troy IX, with various subdivisions.

Until the late 20th century, these layers represented only the layers on the hill of Hisarlik.
Archaeologists following Schliemann picked up the trail of his researches adopting the same fundamental assumptions, culminating in the work and writings of Carl Blegen in the mid-20th century.
In a definitive work, Troy and the Trojans, he summarized the layers names and the dates he had adopted for them.
Without further excavation, Blegen's was the last word.
There were, however, some persistent criticisms not answered to general satisfaction.
Hisarlik, about the size of a football field, was not large enough to have been the mighty city of history.
It was also far inland, yet the general historical tradition suggested it must have been close to the sea.

The issues finally devolved on the necessity for further excavation, which was undertaken by Korfmann starting 1988.
He concentrated on the Roman city, which was not suspected as being over Bronze Age remains.
A Bronze Age city, at low elevations, was discovered beneath it.
As it is unlikely that there were two Troys side by side, the lower city must have been the main seat of residence, to which the upper city served as citadel.
Korfman now referred to the layers of the lower city as associated with the layers of the citadel.
The same layering scheme was applicable.
The lower city was many times the size of the citadel, answering the size objection.

Meanwhile independent geoarchaeological research conducted by taking ground cores over a wide area of the Troad were demonstrating that, in the time of Troy I, "... the sea was right at the foot of 'Schliemann's Trench' during the earliest periods of Troja."
A few thousand years earlier the ridge of Troy was partly surrounded by an inlet of the sea occupying the now agricultural area of the lower Scamander River.
Troy was founded a
What Schliemann actually found as he excavated the hill of Hisarlik somewhat haphazardly were contexts in the soil parallel to the contexts of geologic layers in rock. Exposed rock displays layers of a similar composition and fossil content within a layer discontinuous with other layers above and below it. The layer represents an accumulation of detritus over a continuous time, different from the times of the other layers.
Similarly Schliemann found layers of distinctive soil each containing more or less distinctive artifacts differing often markedly from other layers. He had no ready explanation for the discontinuity between layers, such as "destruction," although this interpretation has sometimes been applied. Presumably "destruction" is to be interpreted to mean some sort of malicious event perpetrated by humans or a natural disaster, such as an earthquake. In most cases no such disaster can be proved. On the contrary, the "many layers illustrate the gradual development of civilization in northwestern Asia Minor."
The discontinuities of culture in different layers might be explained in a number of ways. A settlement might have been abandoned for peaceful reasons, or it might have undergone a renovation phase. These are hypotheses that must be ruled in or ruled out by evidence, or simply be left unruled until evidence should be discovered.
What Schliemann found is that the area now called "the citadel" or "the upper city" was apparently placed on virgin soil. It was protected by fortifications right from the start. The layering effect was caused in part by the placement of new fortifications and new houses over the old. Schliemann called these fortified enclosures "cities" (rightly or wrongly). In his mind the site was composed of successive cities. Like everyone else, he speculated whether a new city represented a different population, and what its relationship to the old was. He numbered the cities I, II, etc., I being on the bottom. Subsequent archaeologists turned the "cities" into layers (rightly or wrongly), named according to the new archaeological naming conventions then being developed. 
The layers of ruins in the citadel at Hisarlik are numbered Troy I – Troy IX, with various subdivisions.
Until the late 20th century, these layers represented only the layers on the hill of Hisarlik. Archaeologists following Schliemann picked up the trail of his researches adopting the same fundamental assumptions, culminating in the work and writings of Carl Blegen in the mid-20th century. In a definitive work, Troy and the Trojans, he summarized the layers names and the dates he had adopted for them. Without further excavation, Blegen's was the last word. There were, however, some persistent criticisms not answered to general satisfaction. Hisarlik, about the size of a football field, was not large enough to have been the mighty city of history. It was also far inland, yet the general historical tradition suggested it must have been close to the sea.
The issues finally devolved on the necessity for further excavation, which was undertaken by Korfmann starting 1988. He concentrated on the Roman city, which was not suspected as being over Bronze Age remains. A Bronze Age city, at low elevations, was discovered beneath it. As it is unlikely that there were two Troys side by side, the lower city must have been the main seat of residence, to which the upper city served as citadel. Korfman now referred to the layers of the lower city as associated with the layers of the citadel. The same layering scheme was applicable. The lower city was many times the size of the citadel, answering the size objection. 
Meanwhile independent geoarchaeological research conducted by taking ground cores over a wide area of the Troad were demonstrating that, in the time of Troy I, "... the sea was right at the foot of 'Schliemann's Trench' during the earliest periods of Troja." A few thousand years earlier the ridge of Troy was partly surrounded by an inlet of the sea occupying the now agricultural area of the lower Scamander River. Troy was founded a
Troy