The White Tower is a central tower, the old keep, at the Tower of London in England. It was built by William the Conqueror during the early 1080s, and subsequently extended. The White Tower was the castle's strongest point militarily, provided accommodation for the king and his representatives, and housed a chapel. Henry III ordered the tower whitewashed in 1240. Today the Tower of London is a museum and visitor attraction. The White Tower now houses the Royal Armouries collections.

A keep is a type of fortified tower built within castles during the Middle Ages by European nobility. Scholars have debated the scope of the word keep, but usually consider it to refer to large towers in castles that were fortified residences, used as a refuge of last resort should the rest of the castle fall to an adversary. The first keeps were made of timber and formed a key part of the motte-and-bailey castles that emerged in Normandy and Anjou during the 10th century; the design spread to England, Portugal, south Italy and Sicily. As a result of the Norman invasion of 1066, use spread into Wales during the second half of the 11th century and into Ireland in the 1170s. The Anglo-Normans and French rulers began to build stone keeps during the 10th and 11th centuries, including Norman keeps, with a square or rectangular design, and circular shell keeps. Stone keeps carried considerable political as well as military importance and could take a decade or more to build.