On June 11, 1144, the Basilica of St Denis was dedicated near Paris. It was the first fully Gothic church. This is an excellent article on the features of Gothic architecture. An excerpt from the introduction to the article:
"The Gothic architecture style found in churches, synagogues, and cathedrals built between approximately 1100 to 1450 CE, stirred the imagination of painters, poets, and religious thinkers in Europe and Great Britain.
From the remarkable great abbey of Saint-Denis in France to the Altneuschul ("Old-New") Synagogue in Prague, Gothic churches were designed to humble man and glorify God. Yet, with its innovative engineering, the Gothic style really was a testament to human ingenuity.
Gothic Beginnings: Medieval Churches and Synagogues
The earliest Gothic structure is often said to be the ambulatory of the abbey of Saint-Denis in France, constructed under the direction of Abbot Suger (1081–1151). The ambulatory became a continuation of the side aisles, providing open access to surround the main altar. How did Suger do it and why? This revolutionary design is fully explained in the Khan Academy video Birth of the Gothic: Abbot Suger and the ambulatory at St. Denis.
Built between 1140 and 1144, St. Denis became a model for most of the late 12th-century French cathedrals, including those at Chartres and Senlis. However, features of the Gothic style are found in earlier buildings in Normandy and elsewhere.
Gothic Engineering
"All of the great Gothic churches of France have certain things in common," wrote American architect and art historian Talbot Hamlin (1889–1956), "—a great love of height, of large windows, and an almost universal use of monumental west fronts with twin towers and great doors between and below them...The whole history of Gothic architecture in France is also characterized by a spirit of perfect structural clarity...to allow all of the structural members to be controlling elements in the actual visual impression."
Gothic architecture does not hide the beauty of its structural elements. Centuries later, American architect Frank Lloyd Wright (1867–1959) praised the "organic character" of Gothic buildings: their soaring artistry grows organically from the honesty of visual construction."