Achilles’ triumphal words that, though the ‘dogs and carrion birds will tear apart Hector’s flesh’, Patroclus will be buried by the Greeks, are particularly severe. Why?
The answer should take Ancient Greek customs into account
Anicient custom required that Hector's body be returned to his family for a proper burial. Achilles leaves Hector's body to be desecrated by the elements... and the animals, but in the end, the gods protect his body from Achilles' desire for revenge, thus, thwarting Achilles intent. Aphrodite stays by the corpse and keeps the animals away from it. She has anointed the body with rosy immortal oil, so that Achilles abuse of the body will not tear the flesh. Apollo uses mist to protect the body from the sun.
Achilles' treatment of Hector's corpse distresses all of the gods, with the exceptions of Poseidon, Hera, and Athena. Hera and Athena still hate Troy for the day that Paris chose Aphrodite over them in a beauty contest of the goddesses. At Apollo's urging, Zeus sends Iris to summon Thetis. He tells Thetis to go to her son and give him Zeus's instructions: he is to accept Priam's ransom, returning the body of Hector so that the Trojans can give Hector a proper burial.
After Hector's body is returned, the people mourn. Andromache, Hecuba, and Helen give speeches praising Hector and mourning his passing. Nine days they mourn, men gathering timber for Hector's funeral pyre all the while. On the tenth day they cremate him. On the eleventh day, they bury his remains, watchful of the Achaeans the whole time, and then they gather to honor Hector with a funeral feast.
http://www.gradesaver.com/iliad/study-guide/summary-books-21-24
