Until very recently, there was no evidence outside the Bible for the existence of King David. There are no references to him in Egyptian, Syrian or Assyrian documents of the time, and the many archaeological digs in the City of David failed to turn up so much as a mention of his name. Then, on July 21, 1993, a team of archaeologists led by Prof. Avraham Biran, excavating Tel Dan in the northern Galilee, found a triangular piece of basalt rock, measuring 23 x 36 cm. inscribed in Aramaic. It was subsequently identified as part of a victory pillar erected by the king of Syria and later smashed by an Israelite ruler. The inscription, which dates to the ninth century bce, that is to say, about a century after David was thought to have ruled Israel, includes the words Beit David (”House” or “Dynasty” of David”). It is the first near-contemporaneous reference to David ever found. It is not conclusive; but it does strongly indicate that a king called David established a dynasty in Israel during the relevant period.
Another piece of significant evidence comes from Dr. Avi Ofer’s archaeological survey conducted in the hills of Judea during the last decade, which shows that in the 11th-10th centuries bce, the population of Judah almost doubled compared to the preceding period. The so-called Rank Size Index (RSI), a method of analyzing the size and positioning of settlements to evaluate to what extent they were a self-contained group, indicates that during this period - David’s supposed period - a strong centre of population existed at the edge of the region. Jerusalem is the most likely candidate for this centre.
To sum up the evidence then: in the tenth century bce, a dynasty was established by David; the population doubled in the hill country of Judah, which acquired a strong central point, probably Jerusalem, a previously settled site that was important enough to be mentioned in Egyptian documents. These facts are certainly consistent with the biblical account; but, before examining the biblical version, we should consider the nature of the Bible and of the historical material it contains.
http://www.jewishvirtuallibrary.org/jsource/History/davidjer.html
Facts are a little different: biblical archeology is just about defunct.
Tel dan at best confirms that there was a Davidian line, but it does nothing to show the size of David’s kingdom. The less gullable will tlel you that the two pieces of the document are not a perfect match and could very well be not one and the same document.