Merlin created the Round Table. Its shape symbolizes the roundness of the universe. He made it for Uther Pendragon, Arthur's father, who gave it to King Laudegraunce, Guinevere's father, when he died. Then when Arthur married Guinevere it was given to him.

The Round Table was first mentioned by the French poet, Wace, in 1155. In that account, it is said that the table was made round so the knights seated around it would be equal and there would be no head of the table to argue over. The table represented the highest Order of Chivalry at King Arthur's court. The knights were the noblest of men who followed a strict code of honor.

In literature, the Round Table varies in size, but the consensus is that it seated 150 and one of them was the Siege Perilous--the danger seat--which no one but the knight destined to achieve the Holy Grail could safely sit in. [1]



This is King Arthur's round table, along with the holy grail on top of it. This table was located in the back garden. [2]

The knights in the Arthurian legend that sat at the Round Table became the main focus of the stories. These knights were
involved with all of the main plots within the story. They earned valor and a name for themselves to be there. All of the knights
there went on quests to earn a spot there because it was not easy just to gain a spot at the Round Table. Technically,
they acted as brothers. However, many things got in the way of this bond. Greed and envy came between many of the
knights at the Round Table. Women were also another factor that caused some knights to fight with one another.
Some knights hated those at the Round Table and fought them because of that, and some
knights fought others at the Round Table.
The following are all knights at the Round Table:

King Arthur Sir Gawain Sir Lancelot Sir Perceval Sir Galahad Sir Bors Sir Kay Bedivere

Lucan the Butler Sir Girflet Sir Yvain Sir Erec Cador Hoel

King Pellinor Tristan (Tristram) Morholt (Marhaus) Palemedes Dinadan

Here is Arthur with Merlin and his Knights of the Round Table (4)




Another picture clearly showing Arthur and his knights at the Round Table. (5)

Knights
There was a total of about 150 knights at the round table. King Laundergaunce who gave the table to Arthur brought 100. Merlin brought 28 knights. The remaining seats were for those knights that proved worthy of such a high position. The kights took great interest in quests. The most important quest was that of the holy grail. The most famous knights were Launcelot, Mordred, Kay, Galahad, and Gawain(6)

Symbolism of the Round Table
The simplest and most obvious symbolism related to he round table is that of its nature of equality. As there is no head to a round table, this gives the presumption that all that sit at the table are equals. Although more subtle, there are some more symbolic significances to the round table. Perhaps the most significant is it's relation to the table at the Last Supper. The Last Supper is depicted to have been round in some pre-renaissance art and Arthur said that it should "resolve a contention among his knights over precedence", which is somewhat similar to the settling of who "accounted the greatest" in heaven that was addressed at the last supper. (7)
It has also been interpreted as a symbol of the world. Its roundness is an obvious reference to the roundness of the planets. Also, it was the only of the "three great tables" that had no spiritual alignment; this makes it more strongly connected to earthly things, such as our planets.
A painting of the Round Table also suggested that it is similar to Fortune's wheel. King Arthur is seen sitting on it, not at it. This may suggest that Arthur's fate is governed by the fortune of the table itself. (7)

Sources:
[1] http://www.arthurian-legend.com/more-about/more-about-arthur-3.php
[2] http://images.google.com/imgres?imgurl=http://news.bbc.co.uk/olmedia/640000/images/_641424_table150.jpg&imgrefurl=http://news.bbc.co.uk/1/hi/scotland/642973.stm&h=180&w=150&sz=9&hl=en&start=3&tbnid=uni0KrazcJ3LfM:&tbnh=101&tbnw=84&prev=/images%3Fq%3Dking%2Barthur%2527s%2Bround%2Btable%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DX
(3) http://www.timelessmyths.com/arthurian/roundtable.html#List
(4)http://members.tripod.com/~midgley/table2.gif
(5) http://metamedia.stanford.edu/imagebin/Knights%20at%20the%20Round%20Table.jpg
(6)http://www.pantheon.org/articles/k/knights_of_the_round_table.html
(7)http://www.csuohio.edu/english/malRT3.html