Abstract
The fortresses of Iran, due to the geographic location and weather conditions have been built to two types of lowland us and mountainous. For this reason, used building materials are different in these two types. Due to the location of the city Jey and southern highway in Isfahan (that have been location of the Caravans passage from the south to the center of Iran), in Gavart area (At the highest point of Mount Gavart) has existed defensive fortress. Due to the full control Gavart fortress on southern highway in Isfahan, this fortress in addition to defensive destination has also been role of the Caravans guide. The research method of this study is based on method of historic, and in this research preliminary data is obtained from field survey. Due to the architecture style and potteries Gavart, this fortress was made in Sassanid period and has probably been used in early Islamic period. The Gavart fortress has a mountain architecture, and hasn’t regular geometric shape. In this fortress, from the top of each tower is seen roof of the front towers. This site probably has other buildings in the lower of the mountain that troglodytic building in lower of the mountain is from these buildings. This fortress is made in three levels and ten architectural parts. The ceramic founds in Gavart fortress aren’t decoration, and they have been practical. In this research, after full description of this building have been answered to the following questions: What period is this building? What is the use of this building?
Keywords: Fortress, Sassanid, Ancient Jey, Gavart.

Introduction
Iran in terms of geographic location (placing on the road of great Khorasan and Silk Road) has always been threatened from different ethnicities and governments. In prehistoric periods, humans have been created fortresses around of villages and cites for defense of animal’s invasions, but later, fortresses created for defense against of invasions humans. Today, in all Iran can be seen remains of strong enclosures residential castles, that indicates are technique Iranian against of aliens.
The fortresses of Iran, due to the geographic location and weather conditions have been built to two types of lowland us and mountainous. For this reason, used building materials are different in these two types. The fortresses located in the plain areas have usually been made to shape of square or rectangular whit circular towers in four corners. The used building materials in these fortresses have been more than mud and adobe brick, and from bricks and plaster have been used less. The walls of these fortresses are made from thick of pies and adobe bricks. In most cases the thickness of these walls are four meters. Inside the fortress are have meandrous alleys, that all of them have led the main passage of the fortress (fortress gateway). In around some of these fortresses is drilled ditch. The mountainous fortresses at the top of the mountains and heights have been made. In construction of mountainous fortresses has usually been used from rubble and mountain stone and river stone with plaster or mortar. Around these types of fortresses have been deep abysses, that impassable these fortresses have been difficult carrying siege devices. At the end of the towers have been congresses. In this research, after full description of this building have been answered to the following questions: What period is this building? What is the use of this building?

Research findings
The Gavart neighborhood is located in 5 km of east of Esfahan city. The height of Gavart is 1710 meters above sea level, and one part of the Ghohab block (from nine blocks of Esfahan). The “Gavart” means nice breeze (this is for stay in the middle of Dasht-e Kavir and Zagros Mountains that is cause interference warm and dry weather with mountainous weather). This area is located in longitude 51° 48ʹ 44ʺ and latitude 32° 38ʹ 01ʺ and in height 1866 m. The architectural traces this collection are 110 m in 40 m. The Gavart fortress has cylindrical towers, long stairs, antemural, wall, cube buildings inside the fortress, and rocky towers. In this fortress has been used highest skill level in build fortress (in terms use of land and natural side effects to increase the strength of the fortress defense). The Gavart fortress is a type of mountainous fortresses that is located in range and the summit of Gavart Mountain. The architectural components of Gavart fortress are includes of the following: stairs of entrance, and architectural sections 1 to 10 (these sections are located in different parts of the fortress). The Gavart fortress has a mountain architecture, and hasn’t regular geometric shape. In this fortress, from the top of each tower is seen roof of the front towers. This site probably has other buildings in the lower of the mountain that troglodytic building in lower of the mountain is from these buildings. On the surface of this fortress are seen ceramic traces to form of scattered. The pottery findings Gavart fortress: fine ware of buff and clinkey, fine ware of red, ware of medium fine and red and clinkey, ware of medium fine and buff, and glazed ware. The ceramic founds in Gavart fortress aren’t decoration, and they have been practical.

Conclusion
The Gavart fortress has been made from rubble and mortar. The location of this fortress in Gavart Mountain has led to invincible this fortress. The elements of main and structural Gavart fortress are including of rocky walls and impassable of mountain. In the one level of this fortress is located architectural part 7. In the second level Gavart fortress is located architectural parts 1, 2, 3, and 8. In the third level of this fortress (that is highest level of Gavart fortress) are located architectural parts 4, 5, 6, 9, and 10. The pottery in this site more is from type of simple.