This type of flavored bread is similar to what is now known as focaccia in Italy today. When the Greeks arrived, they modified the cooking method a bit by placing the seasonings and toppings on the bread before baking, and this became a main course instead of a side dish. This new version of Pizza was quickly adopted by the Romans, and quickly spread across the Roman empire as this coincided with a period of intense Roman expansion. During the Middle Ages and the Renaissance, pizza, or some form of it was eaten and prepared in most of the known civilized world. After the fall of the Roman Empire, the Longobards invaded southern Italy and brought with them the buffalo, and with that cheese, which was added to the pie.
Many different cultures refer to some form of the ancient dish as part of their diet.
However, it was not until the Modern Age that pizza undertook another major transformation. Whether it is a tomato based marinara sauce, or a sliced ripe tomato, most pizza's consumed in America have some form of tomato on them. Tomatoes were first introduced to Italy from South America in 1522. At first the tomato was believed to be poisonous, and was not generally accepted by most Europeans, however the poorer people of the region who regularly subsisted on bread on water alone began adding tomatoes to their yeast dough, and the first modern pizza's were created. During this period, pizza was considered primarily a peasant's dish, but by the 17th century, pizza had achieved a local popularity amongst visitors who would venture into the poorer sections of the countryside to taste pizza prepared by men called pizzaioli.