Passage: There is a widespread but disputed belief, shared by some Barbudans, that the Codringtons set up a human stock farm on Barbuda for the purpose of breeding the strongest, tallest enslaved people. An article in the Annals of the New York Academy of Science has disputed this, stating that the Codringtons considered using Barbuda as a nursery, where slave children would have been raised to work on Antiguan plantations, but this plan was never realized.  Other sources indicate that slaves were, in fact, an export commodity but this was probably due to natural population growth since no new slaves had arrived on the island since the mid-1700s.In any event, the island was certainly an exporter of slaves. An estimate in 1977 by Lowenthal and Clark indicated that between 1779 and 1834, 172 slaves were exported. Most were taken to Antigua, but 37 went to the Leeward and Windward islands, and some went to the southern US. Several slave rebellions took place on the island, with the most serious in 1834-1835.Britain emancipated slaves in most of its colonies in 1834, but that did not include Barbuda, so the island freed its own slaves at that time. For some years afterward, the freed slaves had little opportunity of survival on their own because of limited agricultural land and the lack of available credit to buy some. Therefore, they continued to work on the plantations for nominal wages or lived in shantytowns and worked as occasional labourers. Sugarcane production remained the primary economy for over a century. Effective trade unions were not formed until the 1930s.The first map of Barbuda was made in the second half of the 18th century. At that time there were substantial buildings in the Highland area, a castle in Codrington, a fort on the river, now known as the Martello Tower, and houses at Palmetto Point, Coco Point, and Castle Hill. The map shows eight catching pens for holding captured runaway slaves, indicating that this was a serious problem. There were several defensive cannon batteries around the island...

Question: In what part of the Highlands was there known to be a castle in the 18th century?
Codrington