The canon of classical languages studied in Europe comprises Latin, Greek, and Hebrew (and maybe classical Aramaic). Inspired by this answer mentioning a conlang based on Hittite, my follow-up question is: Are there conlangs based on other languages of the antiquity, like Sumerian, Elamite, Akkadian, Hurrian, or Ancient Egyptian?
I wrote the answer you linked, which talks about Eressilian, a conlang based on the Hittite language, supplemented with loanwords from Arabic, ancient Greek and Persian. I talked there about the Greek influence (which is slight, from the information we have); the Hittite roots are of course much stronger. An example passage given by the creator shows Article 1 of the Universal Declaration of Human Rights, in Hittite and Eressilian:
Hūmant+es antuhsa+es arawa+iya+ya annual+iya kraht(Persian)+a hoquq(Persian/Arabic) anda asanzi hassant+ke. Anda mem+iyan+a wajidan(Persian) asanzi har+ke+ya ēsdu aniya+du adelphotés(Greek)+us katta hūmant+as anda.
Uvẽndesh ãndushesh irawedhadha ãnnuelidha krata ukuk ãnda eshẽnji eshshẽndke. Ãnda mẽvedheva wajidan eshẽnji erkedha ishchu enidhadhu elelpulush kata uvẽndesh ãnda.
I don't have a grasp on the pronunciation of either language, but after attempting to sound it out, the two are quite similar. For instance, the Hittite "antuhsa es" appears similar to the Eressilian "ãndushesh" - both meaning, I believe, "man" or "human".
Goa'uld (Egyptian) (sort of)
This is the "language" spoken by the Goa'uld race in Stargate. It's ostensibly based in ancient Egyptian, drawing from the language and hieroglyphs - appropriate, given that the Goa'uld supposedly ruled Earth as gods, sometimes appearing as the gods of the ancient Egyptians. I keep seeing references to a writing variation called Nakht, which I can't find much information on.
Some (though not much) of the writing uses the Meroitic system. To my (untrained) eye, there don't appear to be a huge amount of similarities (see Meroitic and Goa'uld), but some crossovers show through pretty easily, such as "l"s and "n"s. Those are probably the main Meroitic contributions.
All that said . . . Goa'uld vocabulary is basically made up, and so it's not really a conlang. No attempts were made to keep much linguistic continuity, and so it's not a constructed language as such. There are probably some similarities to ancient Egyptian, but likely not many. I include it here only because its use of some ancient Egyptian hieroglyphs is notable; it appears that an alphabet for the language was indeed constructed.
Irǧeret (Egyptian and Akkadian, with Ugaritic, Arabic and Hebrew influences)
This one seems decently documented by its author. The vocabulary and phonology are derived from Egyptian, although there isn't much vocabulary listed. The organization of nouns - in number and gender - resembles Akkadian. It also contains the Akkadian declensions, with the addition of the dative. In short, the grammar and morphology appears Akkadian, while the vocabulary should be Egyptian. It's an interesting blend.
A note on Proto-Indo-European
A couple of languages have been derived from Proto-Indo-European, the reconstructed common ancestor of Indo-European languages. It's only known indirectly. Therefore, many (though not all) conlangs that are based on it also use words from more recent Indo-European languages. Proto-Indo-European is certainly antique; whether it's "lesser-known" is perhaps another question entirely. That said, it's not a terribly common template, and so I'm listing some Proto-Indo-European languages here for the sake of interest.
- Sambahsa: Sambahsa, an international auxiliary language, appears to be heavily influenced by Proto-Indo-European, primarily through vocabulary. It modifies words from languages ranging from India to Spain, attempting to go back to the languages' common roots.
- Atlantean (Proto-Indo-European): Like Sambahsa, Atlantean is Proto-Indo-European in origin, especially when it comes to vocabulary (grammatically, it is quite different). Notably, it was created by Marc Okrand, the man behind Klingon. According to the linked website, Okrand
took Proto-Indo-European roots and then compared them with language families at various points in time from around the world. Where similarities between words existed, he altered the root or its semantic value to reflect that similarity. By the combination of the PIE roots and by the adoption of new roots from these world languages, he created a vocabulary.
Given that these languages borrow vocabulary from many descendants of Proto-Indo-European, you could argue that they're not directly based in it. However, the intentional linguistic diversity within the family - and the attempts to base words on common similarities that are attributable to Proto-Indo-European - do seem to make these conlangs its descendants.
There's not much info about it online at the moment, but I have been developing Emezila, a conlang based on a mixture of Sumerian and Arabic. It can't really be described as an evolution of Sumerian, but it draws a lot from Sumerian vocabulary and a little from Sumerian grammar.
I've got an ongoing project of creating languages for a world where the Carthaginians won the Second Punic War, where Punic occupies a roughly analogous position to that that Latin has in our world.
Much of it is still only a sketch, but the Late Vulgar Punic (i.e. the analogue of Proto-Romance), Qartydšatim is in a reasonably complete state.
As Carthage was less Imperialist than Rome, I also assume many now-extinct languages would have survived (at least much later than they did in our timeline) so my plans also include descendants of Gaulish and Osco-Umbrian up to the modern day, and Etruscan until Late Antiquity or the Middle Ages (I haven't fully decided).
I also have multiple conlangs derived directly from Proto-Indo-European if that counts as lesser known or antique, although all probably need revisiting as my understanding has improved since I last worked on them. Only one of them has information available online which is Elyŝiskää.