Relative difficulty: Easy-Medium (solved Downs-only)
Theme answers:
- THESIS STATEMENT (16A: Sentence that often appears in the first paragraph of an essay)
- SANITY CHECK (22A: Quick confirmation of feasibility)
- ACID TAB (37A: Dose for an LSD trip)
- BUFFALO BILL (49A: Football player in upstate New York)
Tenochtitlan, also known as Mexico-Tenochtitlan, was a large Mexican altepetl in what is now the historic center of Mexico City. The exact date of the founding of the city is unclear, but the date 13 March 1325 was chosen in 1925 to celebrate the 600th anniversary of the city. The city was built on an island in what was then Lake Texcoco in the Valley of Mexico. The city was the capital of the expanding Aztec Empire in the 15th century until it was captured by the Tlaxcaltec and the Spanish in 1521.
At its peak, it was the largest city in the pre-Columbian Americas. It subsequently became a cabecera of the Viceroyalty of New Spain. Today, the ruins of Tenochtitlan are in the historic center of the Mexican capital. The World Heritage Site of Xochimilco contains what remains of the geography (water, boats, floating gardens) of the Mexica capital.
Tenochtitlan was one of two Mexica āltepētl (city-states or polities) on the island, the other being Tlatelolco. (wikipedia)
The fill is surprisingly weak today. Cheater squares in the corners (NW, SE) and yet you've still got stuff like HAHAS and LIS and SOU and AONE and ANAL. That last one you could easily eliminate by changing TUNA to something like CORA or HORA or even TOGA—I'd take a partial like A GAL or A PAL or something like that over ANAL. It's not an offensive word, of course, it's just ... I dunno. I used it once in a puzzle and I've regretted it ever since. Don't make solvers think about anuses if you don't have to, that's my philosophy. One of them, anyway. Also, RETAIL SHOP kind of clanked. Feels like odd, formal, even dated phrasing. Ditto "mom-and-pop store." The clue did very little to help me get the answer. Needed lots of crosses. Otherwise, though, the Downs-only solve was pretty smooth. As usual, the longer Downs were the harder Downs, with MAIN IDEA and especially RETAIL SHOP taking a bit of work. But ELENA KAGAN (2D: Supreme Court justice appointed by Barack Obama) and BOOBIRDS (39D: Loud and unhappy sports fans, in slang) were gimmes, and nothing in the short stuff was too much of a problem either. As usual, I confused SERB and SLAV (31D: Balkan native), and I could not figure out the "word that can come before" clue (I'm truly bad at these). For 10D: Word before ended, handed or minded (OPEN), I originally wrote in EVEN. I know, "EVEN-ended" is not a thing. I see that now. What else? Oh, I tried every five-letter ancient American civilization I could think of (including OLMEC) before hitting on AZTEC. And I was slightly worried that PESKY might in fact be PESTY (is that a word?) (5D: Irksome).