(Please read from the start)
The first thing to do is to explore the site itself = Abydos and then the Temple in question:
https://en.wikipedia.org/wiki/Abydos,_Egypt#Temple_of_Seti_I
“Abydos (Arabic: ; /əˈbaɪdɒs/ Sahidic Coptic: Ebōt) is one of the oldest cities of ancient Egypt, and also of the eighth nome in Upper Egypt. It is located about 11 kilometres (6.8 miles) west of the Nile at latitude 26° 10' N, near the modern Egyptian towns of el-'Araba el Madfuna and al-Balyana. In the ancient Egyptian language, the city was called Abdju (ꜣbḏw or AbDw). The English name Abydos comes from the Greek Ἄβυδος, a name borrowed by Greek geographers from the unrelated city of Abydos on the Hellespont.
Considered one of the most important archaeological sites in Egypt, the sacred city of Abydos was the site of many ancient temples, including Umm el-Qa'ab, a royal necropolis where early pharaohs were entombed.[1] These tombs began to be seen as extremely significant burials and in later times it became desirable to be buried in the area, leading to the growth of the town's importance as a cult site.
Today, Abydos is notable for the memorial temple of Seti I, which contains an inscription from the nineteenth dynasty known to the modern world as the Abydos King List. It is a chronological list showing cartouches of most dynastic pharaohs of Egypt from Menes until Seti I's father, Ramesses I.
The Great Temple and most of the ancient town are buried under the modern buildings to the north of the Seti temple.[3] Many of the original structures and the artifacts within them are considered irretrievable and lost; many may have been destroyed by the new construction.”
“History
Abydos was occupied by the rulers of the Predynastic period,[4] whose town, temple and tombs have been found there. The temple and town continued to be rebuilt at intervals down to the times of the Thirtieth Dynasty, and the cemetery was in continuous use.
The pharaohs of the First Dynasty were buried in Abydos, including Narmer, who is regarded as the founder of the First Dynasty, and his successor, Aha.[6] It was in this time period that the Abydos boats were constructed. Some pharaohs of the Second Dynasty were also buried in Abydos. The temple was renewed and enlarged by these pharaohs as well. Funerary enclosures, misinterpreted in modern times as great 'forts', were built on the desert behind the town by three kings of the Second Dynasty; the most complete is that of Khasekhemwy.
From the Fifth Dynasty, the deity Khentiamentiu, foremost of the Westerners, came to be seen as a manifestation of the dead pharaoh in the underworld. Pepi I (Sixth Dynasty) constructed a funerary chapel which evolved over the years into the Great Temple of Osiris, the ruins of which still exist within the town enclosure. Abydos became the centre of the worship of the Isis and Osiris cult.
During the First Intermediate Period, the principal deity of the area, Khentiamentiu, began to be seen as an aspect of Osiris, and the deities gradually merged and came to be regarded as one. Khentiamentiu's name became an epithet of Osiris. […]
[…]
Seti I, during the Nineteenth Dynasty, founded a temple to the south of the town in honor of the ancestral pharaohs of the early dynasties; this was finished by Ramesses II, who also built a lesser temple of his own.[5] Merneptah added the Osireion, just to the north of the temple of Seti.”
-
Page 96 –