'Tower' in the Bible

So David took the strong tower for his living-place, naming it the town of David. And David took in hand the building of the town all round, starting from the Millo.

The God of my rock; in him will I trust: he is my shield, and the horn of my salvation, my high tower, and my refuge, my saviour; thou savest me from violence.

He is the tower of salvation for his king: and sheweth mercy to his anointed, unto David, and to his seed for evermore.