Put the port, sugar and spices together in a saucepan (just big enough to fit the 6 pears standing up) and heat up till you prepare the pears. Using a potato peeler, carefully peel the skin off the pears, making sure to leave the stem on the top. If the pears do not stand up, slice a small piece off the bottom. Stir the warmed port, and then put in the pears, standing up, side by side. Reduce the heat and simmer the pears for 30-45 minutes till soft. (Cooking time may vary depending on how firm the pears are)You can check that the pears are cooked by sticking in a sharp knife. If the flesh is soft, they are cooked. The pears will now have taken on the colour of the port, and will be deep burgundy colour. Remove the pears, cinnamon sticks and cloves from the port and put aside. Next, you will need to thicken the port. Take 2 teaspoons of arrowroot and mix them in a small bowl with 1 tablespoon of water. Put half the port mixture back on the heat and add the arrow root, whisking constantly. The port should begin to thicken to a nice glossy sauce as it heats up. Turn off the heat, and put the pears back into the sauce to glaze them. They are now ready to be served. Place the warm pears individually on serving plates and drizzle the thickened port sauce around them on the plate. Alternatively, the pears poached in spiced port can be served chilled with a scoop of ice-cream for a more refreshing dessert.