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Cultural foundations of Gaya had been laid out since the first century B.C., and its culture prospered in the third and fourth B.C. Gaya had been a confederacy of small polities in Nakdong River basin of southern Korea for 600 years before being annexed by Silla in 562 AD. Gaya boasted a flourishing iron culture, earning itself the name of Kingdom of Iron. High quality iron of the times was produced in the present Gimhae area. And, Gaya built up national strength using its stellar mastery of iron.

[Exploring Korean History] 01 Gaya, The Iron Kingdom (with Eng sub)
　

Its influence could be felt in as far as Silla and Japan culture-wise. In those days, Japan had to depend on iron made by Gaya entirely since it didn't have any skill regarding iron making. As Gaya provided raw iron and advanced iron-making skill to small states of Japan, it held mighty influence over Japan in exchange for helping it develop its own iron culture. Iron manufactured by Gaya was imperative in supplying iron to East Asia.
Through a port blessed with natural advantages in then-Gimhae Bay, presently known as Gimhae Plain after the sea dried up, Gaya enjoyed its heyday with its expertise in intermediary trade by exporting iron to Silla, Japan and China and created a unique culture by embracing diverse cultures of others.
The first feature of Gaya culture. Delicate and elaborate craftsmanship Gaya culture was less flamboyant than that of Silla and was distinctive in that it made use of much glass and jade instead of gold and silver. Its cultural heritage, such as earthenware, helmet, armor, saddlery with which people of Gaya used to ride or manage a horse as well as gold crown, features sharper and more delicate craftsmanship compared to Silla. When an old tomb from the latter days of Gaya was unearthed, Gaya's advanced iron making and mastery became pronounced through other excavated goods such as iron arrowhead, iron helmet, sword and other weapons made of iron as well as helmet, armor and accessories.
The second feature of Gaya culture. Creative earthenware and iron culture Gaya's earthenware was made of sand-free mud and created employing a novel method of using a spinning wheel. Such method influenced the way Japan made its earthenware. Its representative piece of work is a vessel in the shape of a warrior on horseback, which was estimated to be made in around the 5th century. This invaluable vessel says much about how advanced Gaya was in terms of making earthenware.

Another artifact is a vessel in the shape of a shallow-draft boat with a flat bottom. Its color, feel of material and patterns embody characteristics of Gaya vessels well. Especially, Wooreuk created Gayageum or a twelve-stringed Korean harp and handed it down to Silla where his music became central to Silla's court music. This clearly shows how advanced Gaya culture had been. After the demise of Gaya, its people were admitted to Silla while members of the royal family Kim of Geumgwan Gaya became Jingol noble classes and Kim Yu-shin of Gaya descent contributed to the unification of the three kingdoms by Silla. After his death, the general received the posthumous appellation of King Heungmu the Great and was revered as one of Silla kings. Descendants of the royal family Kim of Gaya live by one of major family names in Korea, Kim, especially those Gimhae Kim clan.

source: http://prkorea.com/english/e_video/evideo18.htm

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