Street Grid

In urban planning, the grid plan, grid street plan, or gridiron plan is a type of city plan in which streets run at right angles to each other, forming a grid.

Two inherent characteristics of the grid plan, frequent intersections and orthogonal geometry, facilitate movement. The geometry helps with orientation and wayfinding and its frequent intersections with the choice and directness of route to desired destinations.

In ancient Rome, the grid plan method of land measurement was called centuriation. The grid plan dates from antiquity and originated in multiple cultures; some of the earliest planned cities were built using grid plans in Indian subcontinent.

History

Ancient grid plans

By 2600 BC, Mohenjo-daro, major cities of the Indus Valley civilization, were built with blocks divided by a grid of straight streets, running north–south and east–west. Each block was subdivided by small lanes. The cities and monasteries of Sirkap, Taxila and Thimi (in the Indus and Kathmandu Valleys), dating from the 1st millennium BC to the 11th century AD, also had grid-based designs.

A workers' village (2570–2500 BC) at Giza, Egypt, housed a rotating labor force and was laid out in blocks of long galleries separated by streets in a formal grid. Many pyramid-cult cities used a common orientation: a north–south axis from the royal palace and an east–west axis from the temple, meeting at a central plaza where King and God merged and crossed.

Hammurabi king of the Babylonian Empire in the 18th century BC, ordered the rebuilding of Babylon: constructing and restoring temples, city walls, public buildings, and irrigation canals. The streets of Babylon were wide and straight, intersected approximately at right angles, and were paved with bricks and bitumen.

The tradition of grid plans is continuous in China from the 15th century BC onward in the traditional urban planning of various ancient Chinese states. Guidelines put into written form in the Kaogongji during the Spring and Autumn period (770-476 BC) stated: "a capital city should be square on plan. Three gates on each side of the perimeter lead into the nine main streets that crisscross the city and define its grid-pattern. And for its layout the city should have the Royal Court situated in the south, the Marketplace in the north, the Imperial Ancestral Temple in the east and the Altar to the Gods of Land and Grain in the west."

Teotihuacan, near modern-day Mexico City, is the largest ancient grid-plan site in the Americas. The city's grid covered 21 square kilometres(8 square miles).

Perhaps the most well-known grid system is that spread through the colonies of the Roman Empire. The archetypal Roman Grid was introduced to Italy first by the Greeks, with such information transferred by way of trade and conquest.Stanislawski, Dan (1946). "The Grid-Pattern Town", Geog. Rev., xxxvi, pp. 105-120, p. 116.

Ancient Greece

Although the idea of the grid was present in Hellenic societal and city planning, it was not pervasive prior to the 5th century BC. However, it slowly gained primacy through the work of Hippodamus of Miletus (498 – 408 BC), who planned and replanned many Greek cities in accordance with this form.Burns, Ross (2005), ''Damascus: A History'', Routledge, p. 39 The concept of a grid as the ideal method of town planning had become widely accepted by the time of Alexander the Great. His conquests were a step in the propagation of the grid plan throughout colonies, some as far-flung as Taxila in Pakistan, that would later be mirrored by the expansion of the Roman Empire. The Greek grid had its streets aligned roughly in relation to the cardinal points and generally looked to take advantage of visual cues based on the hilly landscape typical of Greece and Asia Minor.Higgins, Hannah (2009) ''The Grid Book''. Cambridge, Massachusetts: MIT Press. p.60. The street grid consisted of ''plateiai'' and ''stenophoi'' (equivalent to Roman '' decumani'' and '' cardines''). This was probably best exemplified in Priene, in present-day western Turkey, where the orthogonal city grid was based on the cardinal points, on sloping terrain that struck views out towards a river and the city of Miletus.

Ancient Rome

The Etruscan people, whose territories in Italy encompassed what would eventually become Rome, founded what is now the city of Marzabotto at the end of the 6th century BC. Its layout was based on Greek Ionic ideas, and it was here that the main east–west and north–south axes of a town (the ''decumanus maximus'' and ''cardo maximus'' respectively) could first be seen in Italy. According to Stanislawski (1946), the Romans did use grids until the time of the late Republic or early Empire, when they introduced '' centuriation'', a system which they spread around the Mediterranean and into northern Europe later on.

The military expansion of this period facilitated the adoption of the grid form as standard: the Romans established '' castra'' (forts or camps) first as military centres; some of them developed into administrative hubs. The Roman grid was similar in form to the Greek version of a grid but allowed for practical considerations. For example, Roman ''castra'' were often sited on flat land, especially close to or on important nodes like river crossings or intersections of trade routes. The dimensions of the ''castra'' were often standard, with each of its four walls generally having a length of . Familiarity was the aim of such standardisation: soldiers could be stationed anywhere around the Empire, and orientation would be easy within established towns if they had a standard layout. Each would have the aforementioned '' decumanus maximus'' and '' cardo maximus'' at its heart, and their intersection would form the forum, around which would be sited important public buildings. Indeed, such was the degree of similarity between towns that Higgins states that soldiers "would be housed at the same address as they moved from ''castra'' to ''castra''". Pompeii has been cited by both Higgins and Laurence as the best preserved example of the Roman grid.

Outside of the castra, large tracts of land were also divided in accordance with the grid within the walls. These were typically per side (called ''centuria''), and contained 100 parcels of land (each called ''heredium'').Gelernter, Mark (2001), ''A history of American architecture: buildings in their cultural and technological context'', p. 15. The ''decumanus maximus'' and ''cardo maximus'' extended from the town gates out towards neighbouring settlements. These were lined up to be as straight as possible, only deviating from their path due to natural obstacles that prevented a direct route.

While the imposition of only one town form regardless of region could be seen as an imposition of imperial authority, there is no doubting the practical reasoning behind the formation of the Roman grid. Under Roman guidance, the grid was designed for efficiency and interchangeability, both facilitated by and aiding the expansion of their empire.

Asia from the first millennium AD

As Japan and the Korean peninsula