The grid plan is a type of city plan in which streets run at right angles to each other, forming a grid.
The grid plan dates from Antiquity and was a common tool of Roman city planning, based originally on its use in military camps. One of the most striking extant Roman grid patterns can be found in the ruins of Timgad in modern-day Algeria. The Roman grid is characterized by a nearly perfectly orthogonal layout of streets, all crossing each other at right angles, and by the presence of two main streets, set at right angles from each other and called the Cardo and the Decumanus. The Cardo and Decumanus are also called the Cardus Maximus and the Decumanus Maximus.
The grid plan was later common in towns of the 18th century or later, which have often been created as part of a city plan, such as the New Town in Edinburgh, or the many towns and cities in Australia, the United States or Canada. Older "new" towns such as those in New England are much less likely to use a grid plan. Often, some of the streets in a grid are numbered (First, Second, etc.), lettered, or arranged in alphabetical order. (Washington, DC has examples of all three, although the alphabetical streets arguably are too far out to be part of the street grid there.)
Arguably the most famous grid plan in history was the plan for New York City formulated in the Commissioners' Plan of 1811, a visionary proposal by the state legislature of New York for the development of most of upper Manhattan.
