Because his name is known, Imhotep is credited with many architectural achievements during the Third Dynasty. Yet only three projects are known with certainty to have been built under his direction: the Step Pyramid of Djoser; the 277- by 544-meter burial complex of Pharoah Djoser surrounded by a high wall featuring one real and fourteen false doors; and the nearby unfinished pyramid of Pharoah Sekhemkhet ("Powerful in Body"; reign 2648-2640 BC), where Imhotep's name is inscribed on the north side of the enclosure wall of the unfinished pyramid.

The next step in the progression toward a "true pyramid" occurred near the end of Imhotep's life during the reign of the early Fourth Dynasty Pharaoh Sneferu at his royal necropolis at Dahshur, where an unknown architect built the so-called Bent Pyramid, circa 2600 BC.

A unique example in pyramid construction, the Bent Pyramid has angled rather than straight sides; the lower part of the pyramid rises from the desert at a 55-degree inclination, while the top section is built at a shallower 43 degree angle, lending the pyramid its very obvious "bent" appearance.

The Bent Pyramid, which Sneferu appears to have abandoned prior to its completion (perhaps the builders realized that the initial angle at the bottom part of the structure was too steep), may have served as an experimental or transitional design between the step-sided pyramids built by during Imhotep's time and the much larger smooth-sided pyramids to come.

Size Matters. Considered the "golden age" of the Old Kingdom, the Fourth Dynasty (2,613 BC– 2,494 BC) was a time of relative peace and prosperity during which trade with neighboring regions provided pharaohs with the leisure to explore artistic and cultural pursuits and the resources to build on a much grander scale.

Credit for completing the first true pyramid goes to Sneferu, who commissioned the Red Pyramid, also known as the North Pyramid, the largest of the three major pyramids located at the Dahshur necropolis, which at the time of its completion was the tallest man-made structure in the world.

The Red Pyramid was followed by the Meidum Pyramid and a number of smaller step pyramids, all of which made Sneferu the most prolific pyramid builder of the era. Egyptologists believe that he may have ordered more stone and brick erected than any other pharaoh.

A much-loved ruler, Sneferu increased the power of the ruling family line by giving official titles and positions to relatives. He conducted military excursions into Sinai, Nubia, Libya, and began trade arrangements with Lebanon for the acquisition of cedar. Keeping a tight rein on lands and estates enabled Sneferu to maintain control over the always ambitious and restive Egyptian nobility.

The earliest-known records of Egyptian contact with her neighbors are found on a large inscribed stone tablet known as the Royal Annals. Fragments of this precious document, which contains records of Egyptian kings from the First Dynasty through the Fifth Dynasty and is among the earliest of all Egyptian texts, are now at the Egyptian Museum in Cairo, at the Petrie Museum in London and the Salinas Regional Archaeological Museum in Palermo, Sicily.

Sneferu's son and successor Pharaoh Khufu (known to the Greeks as Cheops) came to the throne in his twenties and ruled for approximately 23 years (2589 to 2566 BC) and together with his son Khafra (known to the Greeks as Chephren), and his grandson Menkaure (known to the Greeks as Mycerinus), achieved lasting fame in the construction of the Great Pyramid Complex and Great Sphinx at Giza — the oldest and largest of the Seven Wonders of the Ancient World and a UNESCO World Heritage Site.

The Great Pyramids consist of the Great Pyramid of Giza (known as the Great Pyramid and the Pyramid of Cheops or Khufu), which at the time of its completion was the tallest man-made structure in the world, the somewhat smaller Pyramid of Khafre (or Chephren) a few hundred meters to the south-west, and the even smaller Pyramid of Menkaure (or Mykerinos) a few hundred meters further south-west.

The Great Sphinx lies on the east side of the complex, facing east. Current consensus among Egyptologists is that the head of the Great Sphinx is a portrait of Pharaoh Khafre.

Along with these major monuments are a number of smaller satellite edifices, known as "queens" pyramids, causeways, valley pyramids and other royal monuments that appear to be the tombs of high officials and much later burials and monuments (from the New Kingdom onwards).

Builders today cannot help but be impressed with the massive size and remarkable precision of these structures. The base of the Great Pyramid forms a nearly perfect square, with only a 19-centimeter (7.5-inch) difference between its longest and shortest sides, out of a total length of about 230 meters (756 feet). And this huge square is also almost exactly level, a seemingly impossible achievement when building on such a huge scale. When completed, the Great Pyramid rose 146.7 meters (481.4 feet)—or nearly 50 stories high.

Since each pyramid’s core probably contains a hill of stones and rubble, it is not possible to determine the exact number of blocks used to build the structure. Researchers estimate that 2.3 million blocks were used to build the Great Pyramid alone with an average weight of about 2.5 metric tons per block, and the largest block weighing as much as 15 metric tons.

Assembling and organizing the workforce needed to create these pyramids required a centralized government with extensive powers, a high level of sophistication and long periods of prosperity to accomplish such projects. Recent excavations by the American archaeologist Dr. Mark Lehner have uncovered a large city which seems to have been built to house, feed, and supply the workers who built the pyramids.

Although it was long believed that slaves built these monuments — a story that dates back to the Exodus saga in the Bible — recent analysis of the tombs of the workers who oversaw construction on the pyramids, has shown that they were in fact built by members of the peasant class drawn from across Egypt, who worked at Giza and elsewhere in service of the Pharaoh during idle periods, such as during the annual Nile flood, which covered their fields. The immense numbers of specialists needed to build the pyramids (stone cutters, painters, mathematicians, priests, and others) could hardly have been slaves. They were often highly skilled and disciplined workers. Some records from the Fourth Dynasty indicate that each household, regardless of wealth or status, was responsible for providing one worker for such civic projects, and the wealthy could hire skilled artisans to take their places. Such civic duties included not only building projects, but also duties for the temples, libraries, and festivals. Both men and women filled these positions.

Today historians and archaeologists discount the story that appears in Exodus and other sources {such as Herodotus Histories, 2.124-133), which characterize the pyramids as symbols of tyranny built with forced labor, and point to recent discoveries that show these monuments were, in all probability, built by a more or less "willing" population in a highly organized and dedicated manner.

Decline and Collapse. The Fifth Dynasty began with Userkaf ("his Ka (or soul) is powerful.") (reign 2465–2458 BC), who initiated reforms that weakened the Pharaoh and central government.

Egypt's expanding interests in trade goods such as ebony, incense such as myrrh and frankincense, gold, copper and other useful metals inspired the ancient Egyptians to build suitable ships for navigation of the open sea. They traded with Lebanon for cedar and traveled the length of the Red Sea to the Kingdom of Punt, in present-day Ethiopia and Somalia for ebony, ivory and aromatic resins. Ship builders of that era did not use pegs (treenails) or metal fasteners, but relied on rope to keep their ships assembled. Planks and the superstructure were tightly tied and bound together.

After the reigns of Userkaf and Sahure (reign 2487–2475 BC), civil wars arose as the powerful nomarchs (regional governors) no longer belonged to the royal family. The worsening civil conflict undermined unity and energetic government and also caused famines. But regional autonomy and civil wars were not the only causes of this decline. The massive building projects of the Fourth Dynasty had exceeded the capacity of the treasury and populace and, therefore, weakened the kingdom at its roots.

The final blow was a severe drought between 2200 and 2150 BC, which prevented the normal flooding of the Nile and resulted in the decline and collapse of the Old Kingdom, followed by decades of famine and strife. An important inscription on the tomb of Ankhtifi, a nomarch during the early First Intermediate Period, describes the pitiful state of the country when famine stalked the land.

The First Intermediate Period, often described as a “dark period” in ancient Egyptian history, spanned approximately three hundred years after the end of the Old Kingdom from circa 2181 BC to 2055 BC. It included the Seventh, Eighth, Ninth, Tenth, and part of the Eleventh Dynasties. Very little monumental evidence survives from this period, especially towards the beginning of the period. Rule of Egypt was roughly divided between two competing power bases: at Heracleopolis in Lower Egypt, a city just south of the Faiyum region; and at Thebes in Upper Egypt.

It is believed that during this time, the temples were pillaged and violated, their existing artwork was vandalized, and the statues of kings were broken or destroyed as a result of this alleged political chaos. These two kingdoms would eventually come into conflict, with the Theban kings conquering the north, resulting in reunification of Egypt under a single ruler during the second part of the eleventh dynasty.

The causes that brought about the downfall of the Old Kingdom are numerous, but some are merely hypothetical. One reason that is often quoted is the extremely long reign of Pepi II Neferkare, the last major pharaoh of the Sixth Dynasty. He may have had the longest reign of any monarch in history at 94 years (c. 2278 BC – c. 2184 BC), outliving many of his heirs and creating problems with succession in the royal household. The regime of the Old Kingdom disintegrated amidst this disorganization.

Another major problem was the rise in power of the provincial nomarchs. Towards the end of the Old Kingdom the positions of the nomarchs had become hereditary, so families often held onto the position of power in their respective provinces.

As these nomarchs grew increasingly powerful and influential, they became more independent from the king. They erected tombs in their own domains and often raised armies. The rise of these numerous nomarchs inevitably created conflicts between neighboring provinces, often resulting in intense rivalries and warfare between them.

Rise of the Heracleopolitan Kings. After the obscure reign of the seventh and eighth dynasties kings, a group of rulers arose out of Heracleopolis and ruled over Lower Egypt for approximately 594 years. These kings, who comprise the ninth and tenth dynasties, each with nineteen listed rulers, were believed to have descended from Libyan invaders who came into Egypt from the west through the Fayum region. The Heracleopolitan kings eventually overwhelmed the weak Memphite rulers to create the ninth dynasty.

The founder of the Ninth Dynasty, Wankhare Kheti I, is described in legend as an evil and violent ruler who caused much harm to his subjects, was seized with madness and w killed by a crocodile. His successors Wankhare Kheti II and Wankhare Kheti III restored order to the Delta, although their power and influence was never significant compared to that of the Old Kingdom pharaohs.

Herakleopolis Magna, the Greek name of the capital of Heracleopolis, was a cult center of Heryshaf, whom the Greeks identified with Herakles (Hercules).

Legend suggests that a vast labyrinth lay beneath Herakleopolis. During the 1940s, a British archaeological team was rumoured to have discovered the labyrinth but were unable to complete the excavation due to a previously unknown curse, which caused illness among team members and the disappearance of one of the team leaders. The exact location of the labyrinth still remains a mystery.

A 2008 excavation of the site conducted by the Egyptian Supreme Council of Antiquities uncovered burial chambers that had been deliberately burned during ancient times (during military expeditions? by pillagers?). Amid the charred rubble, excavators found finely carved and painted panels decorated with "false doors," including one inscribed with the royal name Khety, that served as portals for communicating with the dead.

Rise of the Theban Kings. Evidence suggests that an invasion of Upper Egypt occurred, simultaneous with the founding of the Heracleopolitan kingdom, which established the Theban line of kings, who comprise the Eleventh and Twelfth Dynasties. This line of kings is believed to have been descendants of Intef or Inyotef (reign ? – 2118 BC), who was the nomarch of Thebes, called the “keeper of the Door of the South”. He is credited for organizing Upper Egypt into an independent ruling body in the south, although he did not claim the title of king. His successors in the Eleventh and Twelfth Dynasties would later do so for him. One of them, Intef II (reign 2118–2069 BC), began the assault on the north at Abydos. Intef III (reign 2069–2061 BC) completed the attack on the north and eventually captured Abydos, moving into Middle Egypt against the Heracleopolitan kings. The first three kings of the Eleventh Dynasty — all named Intef — were also the last three kings of the First Intermediate Period and were succeeded by a line of kings who were all called Mentuhotep. Mentuhotep II (reign 2061–2010 BC), also known as Nebhepetra, eventually defeated the Heracleopolitan kings around 2033 BC.

The end of the First Intermediate Period occurred when Mentuhotep II defeated the Heracleopolitan kings of Lower Egypt and reunited Egypt under a single ruler. This act ushered in a period of great wealth and prosperity known as the Middle Kingdom.