The architecture of Aarhus comprises numerous architectural styles and works from the Middle Ages to present-day. Aarhus has a well-preserved medieval city center with the oldest dwellings dating back to the mid-1500s and some ecclesiastical structures such as St. Clemen's Cathedral and numerous smaller churches that can be traced back to the 1100s. The industrialization of the 19th and 20th centuries left distinctive industrial structures, important National romantic works and some of the best examples of Functionalist architecture in the country. The history of the city as a Viking fort is evidenced in the street layout of the Latin Quarter, the wider Indre By neighborhood testifies to its later role as a Market town and center of commerce while the Frederiksbjerg, Trøjborg and Marselisborg districts showcase the first cohesive urban planning efforts of the early 20th century.

Aarhus is located on the coast in the Bay of Aarhus by the outlet of the Aarhus River where it straddles the hills of forested river valley. It faces the Kattegat in the east, the Brabrand Lake to the west, Riis Forest to the north and the Marselisborg Forests to the south. Aarhus was founded on the north shore of a brackish fjord which over time has sedimentet into a river and lake. The bay provides a natural harbour with a depth of 10 m (33 ft) close to the shore which provided a natural, shielded harbor. Combined with fertile agricultural hinterlands the harbor, and later industrial port, is inextricably linked to the history of Aarhus and her development.

The hilly area consists of a morainal plateau from the last ice age, broken by a complex system of tunnel valleys. The most prominent valleys of this network are the Aarhus Valley in the south, stretching inland east–west with the Aarhus River, Brabrand Lake and Tåstrup Lake and the Egå Valley to the north, with the stream of Egåen, Geding-Kasted Bog and Geding Lake. Most parts of the two valleys have been drained and subsequently farmed, but recently some of the drainage was removed for environmental reasons. The valley system also includes the Lyngbygård River in the west and valleys to the south of the city, following erosion channels from the pre-quaternary. By contrast, the Aarhus River Valley and the Giber River Valley are late glacial meltwater valleys. The coastal cliffs along the Bay of Aarhus consist of shallow tertiary clay from the Eocene and Oligocene (57 to 24 million years ago).

The early Viking settlement consisted mainly of wooden structures and pit-houses of which nothing but archaeological artifacts remain. Wood was the primary building material through the Middle Ages except for ecclesiastical buildings. The first stone churches built in the 11th century were constructed of split and rough granite boulders, limestone, travertine or ashlar such as the crypt church in Our Lady's Priory from 1060. Production of fired brick began in the 13th century and Aarhus Cathedral can be said to be a product of the north European Brick Gothic style resulting from a lack of suitable natural materials commonly used in southern Europe.

Timber-framing was the most common construction method up to the Renaissance and the oldest such buildings date to the 1500s. There are numerous half-timbered structures from the 16th to 19th centuries throughout the city although many have had a brick building facing the street added later as the first fire codes were enforced in the 18th-19th century. Brick gradually became the predominant building material in the 19th century and most of the urban developments from the rapid growth during industrialization is of red brick. Characteristic for Aarhus is the use of yellow bricks in central neighborhoods and buildings such as the Central Station and the area around it including Park Allé, as well as Aarhus University. Reinforced concrete was used for the first time when the Five Sisters were erected in the late 1920s but it didn't become a widespread building material until the 1940s. In the mid-20th century more exotic materials gradually became popular and affordable such as the porphyry used in National Bank Branch in Aarhus from 1926, the Nexø sandstone in St. Mark's Church from 1935 and the marble used for cladding of Aarhus City Hall from 1941.

Archaeological finds indicate that the area around Aarhus may have been inhabited as far back as 100.000 BCE. Stone tools dated to 240.000 BCE have been found in Sønderjylland to the south indicating that the Neanderthals at least strafed the Danish area. More recent artifacts dated to around 100.000 BCE have been found in Himmerland to the north and Lillebælt to the south-east. However, the Weichselian glaciation made it impossible to inhabit most of Denmark between 70.000 BCE and 13.000 BCE as glaciers covered most of peninsular Denmark, including the east coast. Humans returned as the glaciers retreated and evidence points to a hunter gatherer culture until around 4.000 BCE when peoples from the south immigrated north and gradually introduced agriculture. The new agrarian lifestyle meant more permanent settlements and a population boom, starting the Neolithic period.

The area around Aarhus contains many structures from this period, primarily burial sites in the form of tumuli which was a common practice up to the Viking Age. Some 965 round barrows, 24 long barrows and 68 dolmens are registered by the Danish Heritage Agency spread out across Aarhus Municipality. In the early Neolithic the tumuli were simple; a small stone chamber with a single stone for a roof and then covered in earth. Later versions featured larger chambers, passage graves, which could be re-used multiple times. Weathering and ploughing have over time worn down many of the structures but they were officially protected by law in 1937 and remain an omnipresent part of the surrounding landscape.

The early Viking Age settlement was founded on the northern shore of a fjord at the outlet of the Aarhus River. The settlement consisted of pit houses as well as some wooden buildings such as longhouses. Most buildings were about 5 meters by 10 meters and likely had fenced areas for animal husbandry or small-scale farming. Most buildings were built around a wooden frame filled out wattle and daub style and then plastered in mud for protection. Floors were commonly made of wooden planks although some also had simple stamped dirt floors. Straw and reed was the usual material for roofing but turf was also used as well as wood chips in some exclusive buildings. No extant structures remain from this period but there is archaeological evidence both in and around Aarhus. The initial settlement was laid out in elongated fashion along the fjord from Immervad in the west, which functioned as a ford, to the coast in the east where the city bent northwards along the coast towards Riis Skov. North and west of the settlement by the fjord and coast lay a pagan burial site where Bispetorv is today. The fjord further to the west in Viby was the primary harbor where ships were stored in safety from seaborne attacks in close proximity to the king's estate.