C. F. Keil and Franz Delitzsch on 1 Kings 2:10-11

1Ki 2:10-11

After these instructions David died, and was buried in the city of David, i.e., upon Mount Zion, where the sepulchre of David still existed in the time of Christ (Act 2:29).The situation of the tombs of the kings of Judah upon Zion, Thenius has attempted to trace minutely in a separate article in Illgen’s Zeitschrift für die histor. Theol. 1844, i. p. 1ff., and more especially to show that the entrance to these tombs must have been on the eastern slope of Mount Zion, which falls into the valley of Tyropoeon, and obliquely opposite to the spring of Siloah. This is in harmony with the statement of Theodoret (quaest. 6 in iii. Reg.), to the effect that Josephus says, τὸ δὲ μνῆμα (τῆς ταφῆς) παρὰ τὴν Σιλοὰμ εἶναι ἀντροειδὲς ἔχον τὸ σχῆμα, καὶ τῆν βασιλικὴν δηλοῦν πολυτέλειαν; although this statement does not occur in any passage of his works as they have come down to us.

On the length of his reign see 2Sa 5:5.