Rigorous email management system / MON 3-21-22 / Spearlike weapons of medieval times / Jordanian landmark described as a rose-red city half as old as time / Pumpkin seed by another name

Constructor: John Ewbank and Jeff Chen

Relative difficulty: Medium

THEME: BACK-UP SINGER (52A: One helping in a band ... or what can be found in each set of circled letters?) — five-letter one-named singers appear "backed up" (i.e. in reverse) inside of four theme answers:

Theme answers:

• EXPANDED ROLE (20A: Greater responsibility, often as part of a promotion) (singer = LORDE)
• PICKING NITS (26A: Pointing out minuscule annoyances) (singer = STING)
• KHLOÉ KARDASHIAN (38A: Reality star sister of Kim and Kourtney) (singer = DRAKE)
• CHISELED ABS (46A: Goal of some core workouts) (singer = ADELE)

Word of the Day: PETRA (44A: Jordanian landmark described as "a rose-red city half as old as time") —

Petra (Arabic: ٱلْبَتْرَاء, romanized: Al-Batrāʾ; Ancient Greek: Πέτρα, "Rock"), originally known to its inhabitants as Raqmu or Raqēmō is a historic and archaeological city in southern Jordan. It is adjacent to the mountain of Jabal Al-Madbah, in a basin surrounded by mountains forming the eastern flank of the Arabah valley running from the Dead Sea to the Gulf of Aqaba. The area around Petra has been inhabited from as early as 7000 BC, and the Nabataeans might have settled in what would become the capital city of their kingdom as early as the 4th century BC. Archaeological work has only discovered evidence of Nabataean presence dating back to the second century BC, by which time Petra had become their capital. The Nabataeans were nomadic Arabs who invested in Petra's proximity to the incense trade routes by establishing it as a major regional trading hub.

The trading business gained the Nabataeans considerable revenue and Petra became the focus of their wealth. The Nabataeans were accustomed to living in the barren deserts, unlike their enemies, and were able to repel attacks by taking advantage of the area's mountainous terrain. They were particularly skillful in harvesting rainwater, agriculture and stone carving. Petra flourished in the 1st century AD, when its famous Al-Khazneh structure – believed to be the mausoleum of Nabataean king Aretas IV – was constructed, and its population peaked at an estimated 20,000 inhabitants. (wikipedia)

Hello. I have returned from my California vacation ("Spring Break," as it is known). It was lovely, and much needed. My favorite thing in this grid is INBOX ZERO, which has nothing to do with the theme, I realize, but I didn't really enjoy the theme, so let me just focus for a moment on the good parts, OK? I'm surprised someone hasn't made good crossword use of the phrase INBOX ZERO before. It would make a great revealer for some as-yet unimagined crossword. Maybe it's a Schrödinger puzzle, with rebus boxes where "IN" works in one direction and "ZERO" works in the other? That way, you'd have to make the "IN" box "ZERO" (INBOXZERO!)  in order to make sense of the Across (or Down) clues. I like the phrase INBOX ZERO and I like the concept INBOX ZERO and every so often I make it my mission to take my Rex Parker email account down to INBOX ZERO. The juxtaposition of "X" and "Z" is a real treat. So yes, that answer, I liked. The theme ... is interesting, conceptually, I guess. But it's bizarre, too. It has a restriction on it (all the singers are five-letters), but I don't know if the restriction is by design or accident because the the restriction is entirely arbitrary. Why no four-letter singers (STEPPED ASIDE)? Or three-letter (THAI STICK, GREY'S ANATOMY)? Or ... I wanna say 6-letter singers, but I can't really figure out what to do with SELENA (AIRPLANE LESSONS? SPOKANE LESBIANS?). Anyway, it's good, theoretically, that there's a restriction on the theme, but the fact that it's Entirely arbitrary is weird. I get that the Kardashian kinda had to go in the puzzle (what else are you gonna do with EKARD), but that doesn't mean I have to like it. But I guess her name is better than EXPANDED ROLE, which just limps along there, a soulless, dead-weight, flaccid kind of answer. There have to be better ROLEs (or ROLLs!) than that. It's an OK concept, I think, but the singer set is random and many of the theme answers are less than pleasing.